Donor Preference Meets Heterochromatin: Moonlighting Activities of a Recombinational Enhancer in Saccharomyces cerevisiae

During homothallic switching of the mating-type (MAT) gene in Saccharomyces cerevisiae, a- or alpha-specific sequences are replaced by opposite mating-type sequences copied from one of two silent donor loci, HML alpha or HMRa. The two donors lie at opposite ends of chromosome III, approximately 190 and 90 kb, respectively, from MAT. MAT alpha cells preferentially recombine with HMR, while MATa cells select HML. The mechanisms of donor selection are different for the two mating types. MATa cells, deleted for the preferred HML gene, efficiently use HMR as a donor. However, in MAT alpha cells, HML is not an efficient donor when HMR is deleted; consequently, approximately one-third of HO HML alpha MAT alpha hmr delta cells die because they fail to repair the HO endonuclease-induced double-strand break at MAT. MAT alpha donor preference depends not on the sequence differences between HML and HMR or their surrounding regions but on their chromosomal locations. Cloned HMR donors placed at three other locations to the left of MAT, on either side of the centromere, all fail to act as efficient donors. When the donor is placed 37 kb to the left of MAT, its proximity overcomes normal donor preference, but this position is again inefficiently used when additional DNA is inserted in between the donor and MAT to increase the distance to 62 kb. Donors placed to the right of MAT are efficiently recruited, and in fact a donor situated 16 kb proximal to HMR is used in preference to HMR. The cis-acting chromosomal determinants of MAT alpha preference are not influenced by the chromosomal orientation of MAT or by sequences as far as 6 kb from HMR. These data argue that there is an alpha-specific mechanism to inhibit the use of donors to the left of MAT alpha, causing the cell to recombine most often with donors to the right of MAT alpha.

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Saccharomyces cerevisiae Donor Preference During Mating-Type Switching Is Dependent on Chromosome Architecture and Organization

Genetics ◽

10.1534/genetics.106.055392 ◽

2006 ◽

Vol 173 (3) ◽

pp. 1197-1206 ◽

Cited By ~ 22

Author(s):

Eric Coïc ◽

Guy-Franck Richard ◽

James E. Haber

Keyword(s):

Saccharomyces Cerevisiae ◽

Mating Type ◽

Chromosome Architecture ◽

Mating Type Switching ◽

Donor Preference

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Mutations affecting donor preference during mating type interconversion in Saccharomyces cerevisiae.

Genetics ◽

10.1093/genetics/139.4.1495 ◽

1995 ◽

Vol 139 (4) ◽

pp. 1495-1510 ◽

Cited By ~ 2

Author(s):

K S Weiler ◽

L Szeto ◽

J R Broach

Keyword(s):

Saccharomyces Cerevisiae ◽

Chromosome Segregation ◽

Mating Type ◽

Null Allele ◽

Alpha Cells ◽

Opposite Mating Type ◽

Donor Preference ◽

Donor Locus ◽

Type Information ◽

Selection Of

Abstract Homothallic strains of Saccharomyces cerevisiae can convert mating type from a to alpha or alpha to a as often as every generation, by replacing genetic information specifying one mating type at the expressor locus, MAT, with information specifying the opposite mating type. The cryptic mating type information that is copied and inserted at MAT is contained in either of two loci, HML or HMR. The particular locus selected as donor during mating type interconversion is regulated by the allele expressed at MAT. MATa cells usually select HML, and MAT alpha cells usually select HMR, a process referred to as donor preference. To identify factors required for donor preference, we isolated and characterized a number of mutants that frequently selected the nonpreferred donor locus during mating type interconversion. Many of these mutants were found to harbor chromosome rearrangements or mutations at MAT or HML that interfered with the switching process. However, one mutant carried a recessive allele of CHL1, a gene previously shown to be required for efficient chromosome segregation during mitosis. Homothallic strains of yeast containing a null allele of CHL1 exhibited almost random selection of the donor locus in a MATa background but were normal in their ability to select HMR in a MAT alpha background. Our results indicate that Chl1p participates in the process of donor selection and are consistent with a model in which Chl1p helps establish an intrinsic bias in donor preference.

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A Sir2-regulated locus control region in the recombination enhancer of Saccharomyces cerevisiae specifies chromosome III structure

10.1101/558494 ◽

2019 ◽

Author(s):

Mingguang Li ◽

Ryan D. Fine ◽

Manikarna Dinda ◽

Stefan Bekiranov ◽

Jeffrey S. Smith

Keyword(s):

Saccharomyces Cerevisiae ◽

Control Region ◽

Mating Type ◽

Locus Control Region ◽

A Cells ◽

Mating Type Switching ◽

Chromosome Iii ◽

The Right ◽

Donor Preference ◽

Recombination Enhancer

AbstractThe NAD+-dependent histone deacetylase Sir2 was originally identified in Saccharomyces cerevisiae as a silencing factor for HML and HMR, the heterochromatic cassettes utilized as donor templates during mating-type switching. MATa cells preferentially switch to MATα using HML as the donor, which is driven by an adjacent cis-acting element called the recombination enhancer (RE). In this study we demonstrate that Sir2 and the condensin complex are recruited to the RE exclusively in MATa cells, specifically to the promoter of a small gene within the right half of the RE known as RDT1. We go on to demonstrate that the RDT1 promoter functions as a locus control region (LCR) that regulates both transcription and long-range chromatin interactions. Sir2 represses the transcription of RDT1 until it is redistributed to a dsDNA break at the MAT locus induced by the HO endonuclease during mating-type switching. Condensin is also recruited to the RDT1 promoter and is displaced upon HO induction, but does not significantly repress RDT1 transcription. Instead condensin appears to promote mating-type switching efficiency and donor preference by maintaining proper chromosome III architecture, which is defined by the interaction of HML with the right arm of chromosome III, including MATa and HMR. Remarkably, eliminating Sir2 and condensin recruitment to the RDT1 promoter disrupts this structure and reveals an aberrant interaction between MATa and HMR, consistent with the partially defective donor preference for this mutant. Global condensin subunit depletion also impairs mating type switching efficiency and donor preference, suggesting that modulation of chromosome architecture plays a significant role in controlling mating type switching, thus providing a novel model for dissecting condensin function in vivo.Author summarySir2 is a highly conserved NAD+-dependent protein deacetylase and defining member of the sirtuin protein family. It was identified about 40 years ago in the budding yeast, Saccharomyces cerevisiae, as a gene required for silencing of the cryptic mating-type loci, HML and HMR. These heterochromatic cassettes are utilized as templates for mating-type switching, whereby a programmed DNA double-strand break at the MATa or MATα locus is repaired by gene conversion to the opposite mating type. The preference for switching to the opposite mating type is called donor preference, and in MATa cells, is driven by a cis-acting DNA element called the recombination enhancer (RE). It was believed that the only role for Sir2 in mating-type switching was silencing HML and HMR. However, in this study we show that Sir2 also regulates expression of a small gene (RDT1) in the RE that is activated during mating-type switching. The promoter of this gene is also bound by the condensin complex, and deleting this region of the RE drastically changes chromosome III structure and alters donor preference. The RE therefore appears to function as a complex locus control region (LCR) that links transcriptional control to chromatin architecture, and thus provides a new model for investigating the underlying mechanistic principles of programmed chromosome architectural dynamics.

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Yeast Recombination Enhancer Is Stimulated by Transcription Activation

Molecular and Cellular Biology ◽

10.1128/mcb.25.18.7976-7987.2005 ◽

2005 ◽

Vol 25 (18) ◽

pp. 7976-7987 ◽

Cited By ~ 16

Author(s):

Sevinc Ercan ◽

Joseph C. Reese ◽

Jerry L. Workman ◽

Robert T. Simpson

Keyword(s):

Saccharomyces Cerevisiae ◽

Noncoding Rnas ◽

Transcription Activation ◽

Open Chromatin ◽

Conserved Domains ◽

Mating Type Switching ◽

Chromosome Iii ◽

Donor Preference ◽

Recombination Enhancer

ABSTRACT Saccharomyces cerevisiae mating type switching is a gene conversion event that exhibits donor preference. MAT a cells choose HMLα for recombination, and MATα cells choose HMR a. Donor preference is controlled by the recombination enhancer (RE), located between HMLα and MAT a on the left arm of chromosome III. A number of a-cell specific noncoding RNAs are transcribed from the RE locus. Mcm1 and Fkh1 regulate RE activity in a cells. Here we show that Mcm1 binding is required for both the transcription of the noncoding RNAs and Fkh1 binding. This requirement can be bypassed by inserting another promoter into the RE. Moreover, the insertion of this promoter increases donor preference and opens the chromatin structure around the conserved domains of RE. Additionally, we determined that the level of Fkh1 binding positively correlates with the level of donor preference. We conclude that the role of Mcm1 in RE is to open chromatin around the conserved domains and activate transcription; this facilitates Fkh1 binding and the level of this binding determines the level of donor preference.

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