A MUTATION THAT PERMITS THE EXPRESSION OF NORMALLY SILENT COPIES OF MATING-TYPE INFORMATION IN SACCHAROMYCES CEREVISIAE

James E. Haber ¹ and Jeanne P. George ²

¹ Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02254
² Department of Biology, Brandeis University, Waltham, Massachusetts 02254

Studies of heterothallic and homothallic strains of Saccharomyces cerevisiae have led to the suggestion that mating-type information is located at three distinct sites on chromosome 3, although only information at the mating-type (MAT) locus is expressed (Hicks, Strathern and Herskowitz, 1977). We have found that the recessive mutation cmt permits expression of the normally silent copies of mating-type information at the HMa and HM loci. In haploid strains carrying HMa and HM, the cmt mutation allows the simultaneous expression of both a and information, leading to a nonmating ("MATa/MAT") phenotype. The effects of cmt can be masked by changing the mating-type information at HMa or HM. For example, a cell of genotype MATa hma HM cmt has an a mating type, while a MAT hma HM cmt strain is nonmating. Expression of mating-type information at the HM loci can correct the mating and sporulation defects of the mata* and mat10 alleles. Meiotic segregants recovered from cmt/cmt diploids carrying the mat mutations demonstrate that these mutants are not "healed" to normal MAT alleles, as is the case in parallel studies using the homothallism gene HO.—All of the results are consistent with the notion that the HMa and hm alleles both code for information, while HM and hma both code for a information. The cmt mutation demonstrates that these normally silent copies of mating-type and sporulation information can be expressed and that the information at these loci is functionally equivalent to that found at MAT. The cmt mutation does not cause interconversions of mating-type alleles at MAT, and it is not genetically linked to MAT, HMa, HM or HO. In cmt heterozygotes, cmt becomes homozygous at a frequency greater than 1% when the genotype at the MAT locus in mata*/MAT or mat10/MATa.

This article has been cited by other articles:

				S. R. Narala, R. C. Allsopp, T. B. Wells, G. Zhang, P. Prasad, M. J. Coussens, D. J. Rossi, I. L. Weissman, and H. Vaziri SIRT1 Acts as a Nutrient-sensitive Growth Suppressor and Its Loss Is Associated with Increased AMPK and Telomerase Activity Mol. Biol. Cell, March 1, 2008; 19(3): 1210 - 1219. [Abstract] [Full Text] [PDF]

				A. Dasgupta, K. L. Ramsey, J. S. Smith, and D. T. Auble Sir Antagonist 1 (San1) Is a Ubiquitin Ligase J. Biol. Chem., June 25, 2004; 279(26): 26830 - 26838. [Abstract] [Full Text] [PDF]

				A. Naresh, S. Saini, and J. Singh Identification of Uhp1, a Ubiquitinated Histone-like Protein, as a Target/Mediator of Rhp6 in Mating-type Silencing in Fission Yeast J. Biol. Chem., March 7, 2003; 278(11): 9185 - 9194. [Abstract] [Full Text] [PDF]

				C. R. Geyer, A. Colman-Lerner, and R. Brent "Mutagenesis" by peptide aptamers identifies genetic network members and pathway connections PNAS, July 20, 1999; 96(15): 8567 - 8572. [Abstract] [Full Text] [PDF]

				K. Weiss and R. T. Simpson High-Resolution Structural Analysis of Chromatin at Specific Loci: Saccharomyces cerevisiae Silent Mating Type Locus HMLalpha Mol. Cell. Biol., September 1, 1998; 18(9): 5392 - 5403. [Abstract] [Full Text]

				J. S. Smith, C. B. Brachmann, L. Pillus, and J. D. Boeke Distribution of a Limited Sir2 Protein Pool Regulates the Strength of Yeast rDNA Silencing and Is Modulated by Sir4p Genetics, July 1, 1998; 149(3): 1205 - 1219. [Abstract] [Full Text] [PDF]

				S G Holmes and J R Broach Silencers are required for inheritance of the repressed state in yeast. Genes & Dev., April 15, 1996; 10(8): 1021 - 1032. [Abstract] [PDF]

				S W Buck and D Shore Action of a RAP1 carboxy-terminal silencing domain reveals an underlying competition between HMR and telomeres in yeast. Genes & Dev., February 1, 1995; 9(3): 370 - 384. [Abstract] [PDF]

				P Moretti, K Freeman, L Coodly, and D Shore Evidence that a complex of SIR proteins interacts with the silencer and telomere-binding protein RAP1. Genes & Dev., October 1, 1994; 8(19): 2257 - 2269. [Abstract] [PDF]

				H Renauld, O M Aparicio, P D Zierath, B L Billington, S K Chhablani, and D E Gottschling Silent domains are assembled continuously from the telomere and are defined by promoter distance and strength, and by SIR3 dosage. Genes & Dev., July 1, 1993; 7(7a): 1133 - 1145. [Abstract] [PDF]

				M Braunstein, A B Rose, S G Holmes, C D Allis, and J R Broach Transcriptional silencing in yeast is associated with reduced nucleosome acetylation. Genes & Dev., April 1, 1993; 7(4): 592 - 604. [Abstract] [PDF]

				C F Hardy, L Sussel, and D Shore A RAP1-interacting protein involved in transcriptional silencing and telomere length regulation. Genes & Dev., May 1, 1992; 6(5): 801 - 814. [Abstract] [PDF]

				J Singh and A J Klar Active genes in budding yeast display enhanced in vivo accessibility to foreign DNA methylases: a novel in vivo probe for chromatin structure of yeast. Genes & Dev., February 1, 1992; 6(2): 186 - 196. [Abstract] [PDF]

				D J Mahoney, R Marquardt, G J Shei, A B Rose, and J R Broach Mutations in the HML E silencer of Saccharomyces cerevisiae yield metastable inheritance of transcriptional repression. Genes & Dev., April 1, 1991; 5(4): 605 - 615. [Abstract] [PDF]

				J. Diffley and B Stillman Similarity between the transcriptional silencer binding proteins ABF1 and RAP1 Science, November 24, 1989; 246(4933): 1034 - 1038. [Abstract] [PDF]

				K Nasmyth and D Shore Transcriptional regulation in the yeast life cycle Science, September 4, 1987; 237(4819): 1162 - 1170. [Abstract] [PDF]