Vol. 174, No. 10

JOURNAL OF BACTERIOLOGY, May 1992, p. 3411-3415

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Allelism of IMPJ and GAL2 Genes of Saccharomyces cerevisiae CLAUDIA DONNINI,l* TIZIANA LODI,1 ILIANA FERRERO,' ANGELA ALGERI,2 AND PIER PAOLO PUGLISI' Istituto di Genetica, Universita4 di Parma, Viale delle Scienze, 43100 Panna, 1 and Dipartimento di Biologia Evoluzionistica e Sperimentale, Universita di Bologna, Bologna, 2 Italy Received 19 August 1991/Accepted 9 March 1992

In Saccharomyces cerevisiae, conversion of exogenous galactose to endogenous glucose 6-phosphate requires a galactose permease, encoded by the GAL2 gene, and the enzymes of the Leloir pathway (galactokinase, transferase, epimerase, and phopshoglucomutase, encoded by GAL1, GAL7, GAL10 and GAL5, respectively). The expression of these genes is coregulated; it is induced by galactose and repressed by glucose (14, 22). The rapid response of induction is mediated by the activities of at least three trans-acting regulatory genes: GAL4, GAL80, and GAL3 (14). Moreover, glucose inactivates preexisting permease molecules, a process termed catabolite inactivation (12, 14). As originally claimed by Spiegelman (27), galactose utilization in some strains depends on mitochondrial function. The mitochondrial dependency appears to be mediated through the modulation of nuclear gene activity. In fact, (i) strains with mutations of either structural or regulatory genes (GAL1, GAL2, GAL3, GAL4, and GAL5) grow on galactose under respiration-sufficient (RS) conditions but not under respiration-deficient (RD) conditions (1, 9), and (ii) mitochondrial mutants derived from a number of strains that can grow and utilize galactose are unable to use this sugar (1, 8, 10, 34). It has been suggested that gal3 and galS mutants can use galactose because proteins encoded by other genes share some function (GALl with GAL3 and PGMJ with GAL5) (3, 11). The relationship between alternative functions and the mitochondrial function remains to be established (2). Genetic analysis of the strain differences of the mitochondrial mutants indicates that mitochondrial changes alter the activity or expression of nuclear genes involved in the uptake and use of sugars (1, 33). In particular, strains carrying the IMP1 allele can grow on and ferment galactose under both RS and RD conditions or in the presence of a mitochondrial inhibitor such as ethidium bromide or erythromycin. On the contrary, strains carrying the recessive allele impl can grow on and ferment galactose only under RS conditions. In the presence of ethidium bromide, galactose uptake and fermentation are blocked in impl mutants, indicating that the impl mutation makes galactose uptake dependent upon mitochondrial function (1). In an attempt to shed more light on the problem of how *

Corresponding author.

mitochondria intervene in galactose utilization, the IMPI gene was cloned and characterized. The S. cerevisiae strains used in this study and their genotypes are listed in Table 1. Standard yeast genetic procedures for crossing, sporulation, and tetrad analysis were followed (21, 25). Escherichia coli JM83 ara A(lacproAB) rpsL (strA) +80 lacZAM15 and MC1066 (6) were used for plasmid manipulation and preparation. The yeast cells were grown at 28°C in medium M, which contains 2% peptone, 1% yeast extract, and 2% galactose, except where otherwise indicated. E. coli strains were grown in L broth or M9 (20). Ampicillin at a final concentration of 150 ,ug/ml was supplemented for plasmid maintenance. For analysis of adaptation to galactose, cells grown on M medium supplemented with 2% glucose were collected at 4°C in the early stationary phase, washed with cold water, and suspended at an optical density of 580 nm (OD580) of 0.1 in M medium supplemented with 2% galactose with or without 2 p,M antimycin A. Cultures were shaken at 28°C. At various intervals, samples were withdrawn and the OD580 was determined. Where indicated, samples of cultures adapted to grow on galactose were withdrawn and then 2 ,uM antimycin A was added. At appropriate intervals, the OD580 was determined by removing and testing small aliquots. The uptake of radioactive galactose was determined as described previously (23). Total RNAs were isolated from galactose-induced cultures, and formamide-agarose gel electrophoresis was carried out (25). Northern RNA blotting to Hybond N filters (Amersham) and hybridization to 32P-labeled probes were performed by standard techniques (20). Probes were labeled with a nick translation kit (Boehringer). Cloning the IMP) gene. The IMP] gene was cloned by complementation of the impl mutation. Strain KW-5A (trpl impl RD) was transformed as described by Ito et al. (13) with a yeast genomic library cloned in the centromerecontaining plasmid YCBL1. Among 2,500 transformants selected on synthetic medium lacking tryptophan, two clones were able to grow on and ferment 2% galactose. Two different inserts able to complement the impl mutation were isolated from these transformants via E. coli by standard methods (19, 20). Restriction enzyme mapping indicated that these plasmids contained an overlapping insert of 7.2 kb. The shorter plasmid, designated pT7, was further analyzed. 3411

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Cloning and characterization of the previously described Saccharomyces cerevisiae IMP) gene, which was assumed to be a nuclear determinant involved in the nucleomitochondrial control of the utilization of galactose, demonstrate allelism to the GAL2 gene. Galactose metabolism does not necessarily involve the induction of the specific transport system coded by GAL2/IMP1, because a null mutant takes up galactose and grows on it. Data on galactose uptake are presented, and the dependence on ATP for constitutive and inducible galactose transport is discussed. These results can account for the inability of impl/gal2 mutants to grow on galactose in a respiration-deficient background. Under these conditions, uptake was affected at the functional level but not at the biosynthetic level.

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TABLE 1. S. cerevisiae strains Genotype or description

Strain

Source

a imp] leu2 ura3 trpl ade2 Our collection his3 W303-1B al IMP] leu2-3 ura3 trpl ade2 P. Slonimski collection

KW-5A

his3-11,3-15 W303-1A a IMP] leu2-3 ura3 trpl ade2 his3-11,3-15 a IMP1::URA3 leu2-3 trpl LD/1 ade2 his3-11,3-15 STX7-3B a gal2 met] trp3 argl CUPR mal SW a/a- prototroph

P. Slonimski collection

This work

Yeast Genetic Stock Center STX7-3B x W303-1B cross

Sporulation of SW Our collection A. Tzagoloff A. Tzagoloff

Sporulation of LD/1 x E3-24

The restriction map is shown in Fig. 1. Different fragments of the insert were subcloned in the pFL38 plasmid (4) (data not shown). The smallest fragment containing a functional IMP] gene was a 2.5-kb HindIlI-EcoRI fragment designated pHE-3 (Fig. 1). The detailed restriction map of this complementing insert was identical to the restriction map of the GAL2 gene (28). Since both YCBL1 and PFL38 are singlecopy vectors, complementation could not be due to overexpression caused by an excess of episomal plasmid. To confirm that IMP] and GAL2 are identical, a complementation test was performed by crossing K8-6C impl with STX-3B gal2. The diploid obtained did not grow on galactose when the medium was supplemented with ethidium bromide, thus demonstrating that impl and gal2 were allelic. In agreement with this, the pH2-5 plasmid (Fig. 1) complemented the gal2 mutant. In fact, strain SW-liB (ura3 gal2, able to grow on 2% galactose only under RS conditions), when transformed with this plasmid, was able to grow on galactose even in the presence of ethidium bromide. Since IMP] and GAL2 are identical, the gene is referred to below as IMP1IGAL2. Gene disruption. To initiate an analysis of the physiological role of the IMP1/GAL2 gene, we first performed a gene

pT7 p5-4

pA-8

p"-3 S

0

1Kb FIG. 1. Restriction enzyme mapping and complementation analysis of the cloned DNAs containing the IMP] gene. Restriction sites: B, BamHI; H, HindIII; E, EcoRI; Bg, BglII; R, EcoRV. +, complementation of the imp] mutant; -, no complementation.

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a gal2 ura3 met] trp] ade2 ao impi ade2-1 leu2-1 trp5-18 K8-6C D273-10B a prototroph a ubiquinone deficient E3-24 isogenic to D273-1OB a ade2 leu2-3 his3-11 3-15 EG-1A IMP]::URA3, ubiquinone deficient

SW-llB

disruption experiment. The 3.5-kb HindlIl fragment complementing the imp] mutation was cloned in the pUC19 vector (pl-1). The URA3 fragment between the BglII sites of the pFL38 plasmid was inserted in the BglII site of the IMPI! GAL2 gene. The pUC19 vector containing the disrupted IMPI/GAL2 gene was detected by transformation of E. coli MC1066 Ura- (6) and selection of Ura+ transformants on M9 medium. DNA linearized by HindIll was used to transform strain W303-IA IMPI/GAL2 ura3. URA3 transformants that were unable to utilize galactose in the presence of ethidium bromide were selected. One of the clones selected, LD/1, was further analyzed by crossing it with a IMPI/GAL2 ura3 strain. Tetrad analysis of 20 four-spored asci showed that the genes imp] and URA3 cosegregated, indicating that integration of the IMPI] GAL2:: URA3 gene had occurred. The disruption of the IMPJIGAL2 gene was confirmed by Southern blot analysis (data not shown). The null mutation was recessive and was shown to be allelic to impl on the basis of the failure to complement the original K8-6C imp] (1) for growth on galactose under RD conditions. Physiological characterization of the null mutant. We examined the effect of a null IMP1/GAL2 mutation on growth on galactose as the sole carbon source under RS and RD conditions. The phenotype of the null mutant was the same as that of the imp] KW-5A mutant (1; this work). The RS growth of the null mutant was not inhibited by 0.2 to 5% galactose. Transformation of the mutant with plasmid pH2-5, containing the IMP1IGAL2 gene, permitted growth under RD conditions with galactose in the same concentration range. The effects of various mitochondrial inhibitors on the ability to utilize galactose with the null mutant were tested. Oligomycin (10 ,ug/ml), erythomycin (4 mg/ml), antimycin A (2 ,uM), and ethidium bromide (20 ,ug/ml) all prevented growth on galactose (data not shown). The inhibition of growth on galactose could be nonspecifically caused by antimitochondrial drugs. For this reason we used an IMPI/GAL2::URA3 ubiquinone-deficient strain obtained by crossing strain LD/1 IMPI/GAL2::URA3 with the ubiquinone-deficient strain E3-24 (29). The null impl]gal2 ubiquinone-deficient strain EG-1A showed a normal cytochrome profile and, when grown on 0.6% glucose, a respiratory activity corresponding to 5% of that of the wild-type strain grown under the same conditions (data not shown). Strain EG-1A was unable to grow on glycerol, ethanol, or 0.2% or 5% galactose. The growth curves of mutants and wild-type strains on galactose under RS and RD conditions are reported in Fig. 2. The wild-type strain W303-1A, pregrown on glucose, rapidly adapted to grow on galactose (lag time of approximately 2 h). The addition of the respiration inhibitor antimycin A (15) resulted in an adaptative lag time of approximately 18 h, an increase in the doubling time, and a cell yield (OD580) of 4 at the stationary phase; the same strain grown without inhibitor grew to an OD580 of 9. The role of the mitochondria in the induction was supported by the observation that the strain pregrown on galactose immediately resumed growth after antimycin A was added. The impl/gal2 null mutant pregrown on glucose displayed an adaptative lag time of approximately 5 h and an increase in the doubling time (6 h; that of the IMP1IGAL2 parental strain was 3 h). The addition of antimycin A inhibited the growth of both noninduced and induced cultures (Fig. 2A). To compare the effects of antimycin A and ubiquinone

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TIME (HOURS) FIG. 2. Effects of antimycin A and ubiquinone deficiency on growth on galactose. Strains grown on 2% glucose were transferred into complete medium containing 2% galactose with or without 2 ,uM antimycin A. (A) Strain W303-1A (IMPI/GAL2) grown in the absence (0) and presence (m) of the inhibitor; strain LD/1 (IMPJ/GAL2::URA3) grown in the absence (A) and presence (-) of the inhibitor. (B) Strain D273-1OB (IMPIIGAL2) grown in the absence (0) and presence (A) of the inhibitor; strain E3-24 (ubiquinone deficient) grown in the absence (A) and presence (A) of the inhibitor; strain EG-1A (ubiquinone deficient IMP1/GAL2::URA3) grown in the absence (Ol) of the inhibitor. The arrows indicate when antimycin A (AA) was added.

deficiency in an isogenic background, the adaptation to galactose was studied in the D273-1OB strain and in its ubiquinone-deficient derivative, E3-24. The parental strain pregrown on glucose rapidly adaptated to galactose under RS conditions; with the ubiquinone-deficient strain (E3-24) or with the wild type in the presence of antimycin A, similar adaptative lag times, retarded division times, and lower cell yields were observed. Antimycin A added to the E3-24 strain altered neither the adaptation lag time nor the response to growth conditions. On the basis of these results, the effect of antimycin A on growth cannot be attributed to a side effect of the inhibitor; rather, it is due to the inhibition of respiration. As previously reported, the null implIgal2 ubiquinonedeficient strain EG-1A was unable to grow on galactose (Fig. 2B). Effect of inhibiting respiration on galactose transport. The rates of D-[1-14C]galactose uptake as a function of external galactose concentration (Eadie-Hofstee plot) were determined for the impl/gal2 null mutant and the IMPJ/GAL2 parental strain in induced and noninduced cells (Fig. 3A). The plots of galactose uptake in wild-type cells were monophasic for cells grown on glucose and biphasic for cells grown on galactose. The Km value for glucose-grown cells was higher than 200, whereas the Kms for galactose-grown cells were 31 and 0.9 mM for low- and high-affinity processes respectively. The different Km values between of constitutive and induced low-affinity processes indicate that two transport processes are induced by galactose, in agreement with what was reported by Ramos et al. (23). On the other hand, the Eadie-Hofstee plots of galactose uptake by null mutant cells grown on glucose or on galactose were monophasic and the Km corresponded to the Km of the constitutive low-affinity process of wild-type cells (>200 mM, Fig. 3A). Since the impl/gal2 null mutant takes up galactose and grows on it, galactose transport must involve another func-

tion(s) in addition to that encoded by GAL2. Based on the fact of competitive inhibition between galactose and glucose, it has been proposed that, in noninduced cells, galactose is transported as a low-affinity substrate of the glucose carrier (5, 7, 17, 26, 30). If the glucose carrier mediates the process of low-affinity transport, galactose uptake is sufficient to support growth at concentrations as low as 0.2%. Therefore, galactose is a better-than-marginal substrate (18). It remains to be established whether the inhibition of respiration affected galactose transport. The addition of antimycin A decreased inducible and constitutive galactose uptake by approximately 80% (Fig. 3B and C). Since the addition of antimycin A leads to a gradual reduction of the ATP concentration (24), it is possible that low- and highaffinity inducible transport and low-affinity constitutive transport are ATP dependent. An influence of ATP on sugar uptake, mediated by the constitutive glucose carrier, was previously reported for glucose, fructose, and 2-deoxy-Dglucose (24). The results presented here suggest a role of ATP in constitutive galactose transport. These results, however, are in contrast with the previous report that constitutive galactose transport is a low-affinity facilitated diffusion process (7, 31). Other mechanisms of galactose transport in induced cells, including associated phosphorylation (31) and facilitated diffusion (16, 18, 23), have been proposed. The results reported in this paper suggest a role of ATP for lowand high-affinity inducible transport. In principle, ATP may have a dual role in induced cells: regulation of transport and phosphorylation of the sugar. These possibilities remain to be elucidated. The dramatic inhibition of uptake by antimycin A in the null mutant, in which galactose uptake was severely reduced relative to that of the IMP1IGAL2 strain, can account for the inability of impl/gal2 mutants to grow on galactose in an RD background. When antimycin A was added to the wild-type strain, the galactose uptake kinetics at 100 mM was lower than that of

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B

A

C

201 | Km-31

aJ1 -.

0

-S

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9

0

2

1

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7

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9

0.05

0.1

VELOCITY/[tSI FIG. 3. Effect of antimycin A on galactose uptake a's shown by Eadie-Hofstee plots. Uptake rates were calculated for 1 min of uptake by cells (OD580, 22) at 30°C in medium containing 0.66 to 200 mM galactose. (A) Galactose uptake by strain W303-1A (IMP1/GAL2) grown on galactose (O) or glucose (-0) and by strain LD/1 (IMP1IGAL2::URA3) grown on galactose (A) or glucose (A). (B) Galactose uptake in the absence (O) and presence (-) of 2 FLM antimycin A in strain W303-1A pregrown on galactose. (C) Galactose uptake in the absence (A) and presence (A) of 2 FLM antimycin A in strain LD/1 pregrown on galactose.

impl/gal2 mutant in the absence of the inhibitor (data not shown). It is noteworthy that in the correlation between the rate of galactose transport, adaptative lag time, and division time, the higher the rate of galactose uptake (IMP1/GAL2 > impllgal2 > IMPJ/GAL2 in the presence of antimycin A), the shorter the lag time and the division time on galactose. Effect of inhibiting respiration on IMPJIGAL2 gene transcription. Having proven that the inhibition of respiration seriously affected galactose transport in both the null mutant and the parental strain, we carried out experiments to ascertain whether it affected the utilization of galactose by interfering with the expression of the IMPI/GAL2 gene. The transcriptional expression of IMPJIGAL2 under RS and RD conditions was analyzed. Northern analysis of total RNA from galactose-induced cells with the IMPJ/GAL2 gene as a probe indicated that the steady-state levels of the galactoseinducible transcript of the permease encoded by the IMPI/ GAL2 gene were the same under RS and RD conditions (Fig.

IMPI/GAL' ACI

FIG. 4. Northern blot analysis of the IMPJIGAL2 transcripts from strain W303-1A under RS and RD (three successive treatments with 20 ,ug of ethidium bromide per ml) conditions. Total cellular mRNA was prepared from cells grown on 2% galactose. Each lane contained 20 ,ug of total mRNA. Hybridization was carried out with the nick-translated plasmid pI-1 containing IMPIIGAL2 (see the text) as a probe. Subsequent hybridization with a probe specific for yeast actin RNA confirmed that equal amounts of RNA were loaded in all lanes.

4). On this basis, it can be concluded that antimycin A affects uptake only at the functional level and not at the biosynthetic level. We thank E. Petrochilo for providing the yeast genomic library and F. Lacroute for providing the pFL38 plasmid. This research was supported by a grant from the Ministero della Pubblica Istruzione, Italy. REFERENCES 1. Algeri, A. A., L. Bianchi, A. M. Viola, P. P. Puglisi and N. Marmiroli. 1981. IMP1/impl: a gene involved in the nucleomitochondrial control of galactose fermentation in Saccharomyces cerevisiae. Genetics 97:27-44. 2. Bhat, P. J., and J. E. Hopper. 1991. The mechanism of inducer formation in gal3 mutants of the yeast galactose system is independent of normal galactose metabolism and mitochondrial respiratory function. Genetics 128:233-239. 3. Bhat, P. J., D. Oh, and J. E. Hopper. 1990. Analysis of the GAL3 signal transduction pathway activating GAL4 proteindependent transcription in Saccharomyces cerevisiae. Genetics 125:281-291. 4. Bonneaud, N., 0. Ozier-Kalogeropoulos, G. Li, M. Labouesse, L. Minvielle-Sebastia, and F. Lacroute. 1991. A family of low and high copy replicative, integrative and single-stranded S. cerevisiaelE. coli shuttle vectors. Yeast 7:609-615. 5. Burger, M., L. Hejmova, and A. Kleinzeller. 1959. Transport of some mono- and di-saccharides into yeast cells. Biochem. J. 71:233-242. 6. Casabadan, M. J., A. Martinez-Arias, S. K. Shapira, and J. Chou. 1983. ,-Galactosidase gene fusions for analysing gene expression in Escherichia coli and yeast. Methods Enzymol. 100:293-308. 7. Cirillo, V. P. 1968. Relationship between sugar structure and competition for the sugar transport system in baker's yeast. J. Bacteriol. 95:603-611. 8. Donnini, C., T. Lodi, I. Ferrero, and P. P. Puglisi. 1992. IMP2, a nuclear gene controlling the mitochondrial dependence of galactose, maltose and raffinose utilization in Saccharomyces cerevisiae. Yeast 8:83-93.

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22. Oh, D., and J. E. Hopper. 1990. Transcription of a yeast phosphoglucomutase isozyme gene is galactose inducible and glucose repressible. Mol. Cell. Biol. 10:1415-1422. 23. Ramos, J., K. Szkutnicka, and V. P. Cirillo. 1989. Characteristics of galactose transport in Saccharomyces cerevisiae cells and reconstituted lipid vesicles. J. Bacteriol. 171:3539-3544. 24. Schuddemat, J., P. J. A. van den Broek, and J. van Steveninck. 1988. The influence of ATP on sugar uptake mediated by the constitutive glucose carrier of Saccharomyces cerevisiae. Biochim. Biophys. Acta 937:81-87. 25. Sherman, F., G. R. Fink, and J. B. Hicks. 1982. Methods in yeast genetics. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. 26. Sols, A. 1967. Regulation of carbohydrate transport and metabolism in yeast, p. 47-66. In A. K. Mill and H. Krebs (ed.), Aspects of yeast metabolism. Blackwell Scientific Publishers, Oxford. 27. Spiegelman, S. 1945. The effect of anaerobiosis on adaptation to enzyme formation. J. Cell. Comp. Physiol. 26:121-131. 28. Tschopp, J. F., S. D. Emr, C. Field, and R. Schekman. 1986. GAL2 codes for a membrane-bound subunit of the galactose permease in Saccharomyces cerevisiae. J. Bacteriol. 166:313318. 29. Tzagoloff, A., A. Akai, and R. B. Needleman. 1975. Assembly of the mitochondrial membrane system. Characterization of nuclear mutants of Saccharomyces cerevisiae with defects in mitochondrial ATPase and respiratory enzymes. J. Biol. Chem. 250:8228-8235. 30. van Steveninck, J. 1972. Transport and transport-associated phosphorylation of galactose in Saccharomyces cerevisiae. Biochim. Biophys. Acta 274:575-583. 31. van Steveninck, J., and E. C. Dawson. 1968. Active and passive galactose transport in yeast. Biochim. Biophys. Acta 150:47-55. 32. van Steveninck, J., and A. Rothstein. 1965. Sugar transport and metal binding in yeast. J. Gen. Physiol. 49:235-246. 33. Wilkie, D., and I. H. Evans. 1982. Mitochondria and the yeast cell surface: implications for carcinogenesis. Trends Biochem. Sci. 4:147-151. 34. Wilkie, D., I. H. Evans, V. Egilsonn, E. S. Diala, and D. Collier. 1983. Mitochondria, cell surface, and carcinogenesis. Int. Rev. Cytol. 15(Suppl.):157-189.

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9. Douglas, H. C., and D. C. Hawthorne. 1964. Enzymatic expression and genetic lingake of genes controlling galactose utilization in Saccharomyces. Genetics 49:837-844. 10. Evans, I. H., and D. Wilkie. 1976. Mitochondrial factors in the utilization of sugars in Saccharomyces cerevisiae. Genet. Res. 27:89-93. 11. Fraenkel, D. G. 1982. Carbohydrate metabolism, p. 1-37. In J. N. Strathern, E. W. Jones, and J. R. Broach (ed.), The molecular biology of the yeast Saccharomyces: metabolism and gene expression. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. 12. Holzer, H. 1976. Catabolite inactivation in yeast. Trends Biochem. Sci. 1:178-181. 13. Ito, H., Y. Fukuda, K. Murata, and A. Kimura. 1983. Transformation of intact cells treated with alkali cations. J. Bacteriol. 153:163-168. 14. Johnston, M. 1987. A model fungal gene regulatory mechanism: the GAL genes of Saccharomyces cerevisiae. Microbiol. Rev. 51:458-476. 15. Kaniuga, Z., J. Bryla, and E. C. Slater. 1969. Inhibitors around the antimycin-sensitive site in the respiratory chain, p. 282-300. In T. Bucher and H. Sies (ed.), Inhibitors-tools in cell research. Springer-Verlag KG, Berlin. 16. Kotyk, A., and C. Haskovecs. 1968. Properties of the sugar carrier in baker's yeast. III. Induction of the galactose carrier. Folia Microbiol. 13:12-19. 17. Kotyk, A., and D. Michaljanicova. 1974. Nature of the uptake of galactose, D-glucose and a-methyl-D-glucose by Saccharomyces cerevisiae. Biochim. Biophys. Acta 322:104-113. 18. Kuo, S. C., and V. P. Cirillo. 1970. Galactose transport in Saccharomyces cerevisiae. III. The characteristics of galactose uptake in transferaseless cells: evidence against transport associated phosphorylation. J. Bacteriol. 103:679-685. 19. Mandel, H., and A. Higa. 1970. Calcium dependent bacteriophage DNA infection. J. Mol. Biol. 53:159-162. 20. Maniatis, T., E. F. Fritsch, and J. Sambrook. 1982. Molecular cloning: a laboratory manual. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. 21. Mortimer, R. K., and D. C. Hawthorne. 1969. Yeast genetics, p. 385-460. In A. H. Rose and J. S. Harrison (ed.), The yeasts, vol. 1. Academic Press, Inc., New York.

NOTES

Allelism of IMP1 and GAL2 genes of Saccharomyces cerevisiae.

Cloning and characterization of the previously described Saccharomyces cerevisiae IMP1 gene, which was assumed to be a nuclear determinant involved in...
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