Ruskin B, Fink G R
Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142.
Genetics. 1993 May;134(1):43-56. doi: 10.1093/genetics/134.1.43.
Tandem inverted repeats (TIRs or hairpins) of 30 and 80 base-pair unit lengths are unstable mitotically in yeast (Saccharomyces cerevisiae). TIR instability results from deletions that remove part or all of the presumed hairpin structure from the chromosome. At least one deletion endpoint is always at or near the base of the hairpin, and almost all of the repaired junctions occur within short direct sequence repeats of 4 to 9 base pairs. The frequency of this event, which we call "hairpin excision," is influenced by chromosomal position, length of the inverted repeats, and the distance separating the repeat units; increasing the distance between the inverted repeats as little as 25 base pairs increases their chromosomal stability. The frequency of excision is not affected by representative rad mutations, but is influenced by mutations in certain genes affecting DNA synthesis. In particular, mutations in POL1/CDC17, the gene that encodes the large subunit of DNA polymerase I, increase the frequency of hairpin deletions significantly, implicating this protein in the normal maintainance of genomic TIRs.
30个碱基对和80个碱基对单位长度的串联反向重复序列（TIRs或发夹结构）在酵母（酿酒酵母）中进行有丝分裂时不稳定。TIR的不稳定性源于缺失，这些缺失会从染色体上移除部分或全部假定的发夹结构。至少有一个缺失端点总是在发夹的基部或其附近，并且几乎所有修复后的连接点都出现在4至9个碱基对的短直接序列重复内。我们将此事件的频率称为“发夹切除”，它受染色体位置、反向重复序列的长度以及重复单元之间的距离影响；将反向重复序列之间的距离增加仅25个碱基对就会增加它们在染色体上的稳定性。切除频率不受代表性rad突变的影响，但受影响DNA合成的某些基因中的突变影响。特别是，编码DNA聚合酶I大亚基的基因POL1/CDC17中的突变会显著增加发夹缺失的频率，这表明该蛋白参与了基因组TIRs的正常维持。
