Lundquist R C, Olivera B M
Cell. 1982 Nov;31(1):53-60. doi: 10.1016/0092-8674(82)90404-4.
We show that displaced single-stranded overhangs are transiently generated and destroyed during nick translation by E. coli DNA polymerase I. Evidence that hyper-rec mutants have an increased frequency of such overhang structures is discussed. The transient generation of overhangs may be significant for general recombination. The 5' leads to 3' exonuclease activity of polymerase I specifically hydrolyzes such overhangs to yield a nick. Overhangs are generated by polymerization, but after every polymerization step, either polymerase or exonuclease can act--55% of the time, polymerization occurred first. At this frequency overhangs of greater than or equal to 12 nucleotides are generated every 1300 nucleotides polymerized. We suggest that many DNA strand discontinuities are displaced single-stranded overhangs, rather than gaps or simple nicks.
我们发现，在大肠杆菌DNA聚合酶I进行切口平移的过程中，单链悬垂会短暂地产生和消失。文中讨论了高重组突变体中此类悬垂结构频率增加的证据。悬垂的短暂产生可能对一般重组具有重要意义。聚合酶I的5'→3'核酸外切酶活性会特异性地水解此类悬垂，从而产生一个切口。悬垂是由聚合作用产生的，但在每一步聚合之后，聚合酶或核酸外切酶都可能发挥作用——55%的情况下，聚合作用首先发生。以这种频率，每聚合1300个核苷酸就会产生大于或等于12个核苷酸的悬垂。我们认为，许多DNA链的不连续处是单链悬垂，而非缺口或简单的切口。
