Human Rad51 protein can form homologous joints in the absence of net strand exchange.
The eukaryotic homologs of RecA protein are central enzymes of recombination and repair, and notwithstanding a high degree of conservation they differ sufficiently from RecA to offer insights into mechanisms and biological roles. The yield of DNA strand exchange reactions driven by both Escherichia coli RecA protein and its human homolog HsRad51 protein was inversely related to the GC content of oligonucleotide substrates, but at any given GC composition, HsRad51 promoted less exchange than RecA. When 40% of bases were GC pairs, the rate constant for strand exchange by HsRad51 was unmeasurable, whereas the rate constants for homologous pairing were unaltered relative to more AT-rich DNA. The ability of HsRad51 to form joints in the absence of net strand exchange was confirmed by experiments in which heterologous blocks at both ends of linear duplex oligonucleotides produced joints that instantly dissociated upon deproteinization. These findings suggest that HsRad51 acting alone on human DNA in vivo is a pairing protein that cannot form extensive heteroduplex DNA.
Gupta
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Department of Genetics and the Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, Connecticut 06510, USA. rgupta@biomed.med.yale.edu
Folta-Stogniew
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Radding
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D020137:Base Pair Mismatch; D002384:Catalysis; D004277:DNA, Single-Stranded / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D003850:Deoxyribonuclease I / Q000378:metabolism; D006801:Humans; D015636:Magnesium Chloride / Q000494:pharmacology; D008970:Molecular Weight; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000378:metabolism; D011487:Protein Conformation; D051135:Rad51 Recombinase; D011938:Rec A Recombinases / Q000378:metabolism; D011995:Recombination, Genetic
D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D009841:Oligonucleotides; D015636:Magnesium Chloride; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D011938:Rec A Recombinases; D003850:Deoxyribonuclease I