Department of Developmental Biology, Wennergren Institute, Stockholm University, Stockholm, Sweden.
Genetics. 2010 Apr;184(4):999-1011. doi: 10.1534/genetics.110.114678. Epub 2010 Feb 5.
To explore the similarities and differences of regulatory circuits among budding yeasts, we characterized the role of the unscheduled meiotic gene expression 6 (UME6) gene in Kluyveromyces lactis. We found that Ume6 was required for transcriptional silencing of the cryptic mating-type loci HMLalpha and HMRa. Chromatin immunoprecipitation (ChIP) suggested that Ume6 acted directly by binding the cis-regulatory silencers of these loci. Unexpectedly, a MATa ume6 strain was mating proficient, whereas a MATalpha ume6 strain was sterile. This observation was explained by the fact that ume6 derepressed HMLalpha2 only weakly, but derepressed HMRa1 strongly. Consistently, two a/alpha-repressed genes (MTS1 and STE4) were repressed in the MATalpha ume6 strain, but were expressed in the MATa ume6 strain. Surprisingly, ume6 partially suppressed the mating defect of a MATa sir2 strain. MTS1 and STE4 were repressed in the MATa sir2 ume6 double-mutant strain, indicating that the suppression acted downstream of the a1/alpha2-repressor. We show that both STE12 and the MATa2/HMRa2 genes were overexpressed in the MATa sir2 ume6 strain. Consistent with the idea that this deregulation suppressed the mating defect, ectopic overexpression of Ste12 and a2 in a MATa sir2 strain resulted in efficient mating. In addition, Ume6 served as a block to polyploidy, since ume6/ume6 diploids mated as pseudo a-strains. Finally, Ume6 was required for repression of three meiotic genes, independently of the Rpd3 and Sin3 corepressors.
为了探究芽殖酵母调控回路的异同，我们对乳酸克鲁维酵母中的非预期减数分裂基因表达 6（UME6）基因的作用进行了研究。我们发现 Ume6 对于隐性交配型基因座 HMLα 和 HMRa 的转录沉默是必需的。染色质免疫沉淀（ChIP）表明 Ume6 通过结合这些基因座的顺式调控沉默子直接发挥作用。出乎意料的是，MATα ume6 菌株具有交配能力，而 MATα ume6 菌株是不育的。这一观察结果可以用以下事实来解释：ume6 仅弱地去阻遏 HMLα2，但强烈地去阻遏 HMRa1。一致地，两个 a/α 抑制基因（MTS1 和 STE4）在 MATα ume6 菌株中受到抑制，但在 MATa ume6 菌株中表达。令人惊讶的是，ume6 部分抑制了 MATa sir2 菌株的交配缺陷。在 MATa sir2 ume6 双突变菌株中，MTS1 和 STE4 受到抑制，表明抑制作用发生在 a1/α2 抑制剂的下游。我们表明，STE12 和 MATa2/HMRa2 基因在 MATa sir2 ume6 菌株中均过表达。与这种去调控抑制交配缺陷的观点一致，在 MATa sir2 菌株中外源过表达 Ste12 和 a2 导致有效的交配。此外，Ume6 作为多倍体的阻断物，因为 ume6/ume6 二倍体作为假 a 菌株进行交配。最后，Ume6 独立于 Rpd3 和 Sin3 共抑制因子抑制三个减数分裂基因。
