Bianco P R, Kowalczykowski S C
Sections of Microbiology and of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA.
Proc Natl Acad Sci U S A. 1997 Jun 24;94(13):6706-11. doi: 10.1073/pnas.94.13.6706.
The RecBCD enzyme of Escherichia coli functions in the seemingly disparate roles of homologous recombination and the degradation of DNA. Which of these two roles it assumes is regulated by the 8-base recombination hotspot, Chi. Using double-stranded DNA substrates that are heteroduplex at the Chi locus we have established the determinants for Chi recognition. Our results show that an actively translocating RecBCD enzyme requires only the sequence information in the 5'-GCTGGTGG-3'-containing strand to recognize and to be regulated by Chi. Furthermore, the RecBCD enzyme can translocate through DNA heteroduplex bubbles as large as 22 bases, and still recognize a Chi sequence embedded in this region. This implies that recognition of Chi occurs following the unwinding of the DNA.
大肠杆菌的RecBCD酶在同源重组和DNA降解这两个看似不同的过程中发挥作用。它承担这两种作用中的哪一种,是由8碱基的重组热点Chi调控的。利用在Chi位点呈异源双链的双链DNA底物,我们确定了Chi识别的决定因素。我们的结果表明,一个正在积极移位的RecBCD酶只需要含5'-GCTGGTGG-3'链中的序列信息来识别Chi并受其调控。此外,RecBCD酶能够穿过长达22个碱基的DNA异源双链泡,并仍然识别嵌入该区域的Chi序列。这意味着Chi的识别发生在DNA解旋之后。