350회 The RecA protein is essential for the extreme radiation-resistanc…
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작성자 : 관리자 날짜 : 작성일03-03-13 21:36 조회 : 3,334회본문
350회
연사 : 김 종 일, 서울여자대학교 식품미생물공학과
제목: The RecA protein is essential for the extreme radiation-resistance of Deinococcus radiodurans
Abstract
Deinococcus radiodurans (Dr) is part of a small family that are the most radiation-resistant organisms known. Although this organism efficiently repairs many types of severe DNA damage, resistance to ionizing radiation is especially remarkable. Dr is able to survive exposures to gamma radiation in excess of 1.7 Mrads without lethality or induced mutation and can survive hundreds of irradiation-induced DNA double-stranded breaks per haploid genome. The mechanisms underlying this organism's very efficient DNA repair seem to be complex but remain poorly understood.
The RecA protein of Deinococcus radiodurans (Dr) is essential for the extreme radiation resistance of this organism. It forms helical filaments on DNA, hydrolyzes ATP and dATP, and promotes DNA strand exchange. Its binding to double-stranded DNA (dsDNA) is more facile than that observed for the Ec RecA protein. The Dr RecA protein hydrolyzes dATP faster than ATP, and dATP facilitates its displacement of Ec SSB protein from ssDNA. When both ss- and dsDNA are present in a solution, the Dr RecA protein binds preferentially to the dsDNA. This property is in stark contrast to the DNA-binding properties of the Ec RecA protein.
The RecA protein of Escherichia coli, and all filament-forming homologues identified to date, promote DNA strand exchange by a common, ordered pathway. A filament is first formed on single-stranded DNA, followed by uptake of the duplex substrate. These proteins are thereby targeted to single-strand gaps and tails where recombinational DNA repair is required. The observed course of DNA strand exchange promoted by the RecA protein from the extremely radioresistant bacterium Deinococcus radiodurans is the exact inverse of this established pathway. This reaction lies at the heart of a remarkably efficient system for the repair of DNA damage.
