Polar Destabilization of DNA Duplexes with Single-Stranded Overhangs by the Deinococcus radiodurans SSB Protein

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• 作者：Julie M. Eggington ; Alexander G. Kozlov ; Michael M. Cox ; Timothy M. Lohman
• 刊名：Biochemistry
• 出版年：2006
• 出版时间：December 5, 2006
• 年：2006
• 卷：45
• 期：48
• 页码：14490 - 14502
• 全文大小：582K
• 年卷期：v.45,no.48(December 5, 2006)
• ISSN：1520-4995

文摘

The Deinococcus radiodurans SSB protein has an occluded site size of 50 ± 2 nucleotides onssDNA but can form a stable complex with a 26-30-nucleotide oligodeoxynucleotide using a subset ofits four ssDNA binding domains. Quantitative estimates of D. radiodurans SSB protein in the D.radiodurans cell indicate approximately 2500-3000 dimers/cell, independent of the level of irradiation.At biologically relevant concentrations, when bound at single-strand-double-strand DNA junctions invitro, D. radiodurans SSB protein has a limited capacity to displace the shorter strand of the duplex,permitting it to bind to single-strand extensions shorter than 26-30 nucleotides. The capacity to displacethe shorter strand of the duplex shows a pronounced bias for extensions with a free 3' end. The Escherichiacoli SSB protein has a similar but somewhat less robust capacity to displace a DNA strand annealedadjacent to a single-strand extension. These activities are likely to be relevant to the action of bacterialSSB proteins in double-strand break repair, acting at the frayed ends created by ionizing radiation.