Kassir Y, Simchen G
Genetics. 1985 Mar;109(3):481-92. doi: 10.1093/genetics/109.3.481.
Mutations leading to expression of the silent HMRa information in Saccharomyces cerevisiae result in sporulation proficiency in mata1/MAT alpha diploids. An example of such a mutation is sir5-2, a recessive mutation in the gene SIR5. As expected, haploids carrying the sir5-2 mutation are nonmaters due to the simultaneous expression of HMRa and HML alpha, resulting in the nonmating phenotype of an a/alpha diploid. However, sir5-2/sir5-2 mata1/MAT alpha diploids mate as alpha yet are capable of sporulation. The sir5-2 mutation is unlinked to sir1-1, yet the two mutations do not complement each other: mata1/MAT alpha sir5-2/SIR5 SIR1/sir1-1 diploids are capable of sporulation. In this case, recessive mutations in two unlinked genes form a mutant phenotype, in spite of the presence of the normal wild-type alleles. The PAS1-1 mutation, Provider of a Sporulation function, is a dominant mutation tightly linked to HMRa. PAS1-1 does not affect the mating ability of a strain, yet it allows diploids lacking a functional MATa locus to sporulate. It is proposed that PAS1-1 leads to partial expression of the otherwise cryptic a1 information at HMRa.
导致酿酒酵母中沉默的HMRa信息得以表达的突变会使mata1/MATα二倍体具有产孢能力。此类突变的一个例子是sir5-2，它是SIR5基因中的一个隐性突变。正如预期的那样，携带sir5-2突变的单倍体由于HMRa和HMLα的同时表达而成为非交配型，从而产生a/α二倍体的非交配表型。然而，sir5-2/sir5-2 mata1/MATα二倍体作为α型进行交配，但能够产孢。sir5-2突变与sir1-1不连锁，但这两个突变不能相互互补：mata1/MATα sir5-2/SIR5 SIR1/sir1-1二倍体能够产孢。在这种情况下，尽管存在正常的野生型等位基因，但两个不连锁基因中的隐性突变形成了一种突变表型。PAS1-1突变，即产孢功能提供者，是一种与HMRa紧密连锁的显性突变。PAS1-1不影响菌株的交配能力，但它能使缺乏功能性MATa位点的二倍体产孢。有人提出，PAS1-1会导致HMRa处原本隐秘的a1信息部分表达。
