Beta protein of bacteriophage lambda promotes renaturation of DNA

The protein encoded by the red beta gene of bacteriophage lambda was found to promote reannealing of complementary single strands of DNA. Reannealing activity was optimal at pH 6.0 and required a divalent cation. A threshold temperature of at least 15 degrees C was necessary in order to detect activity. The reaction was linear with time for about 20 min, but the extent of reaction was dependent upon the amount of beta protein added. Reannealing of complementary single strands was confirmed by measuring increased lability of DNA to lambda exonuclease. When protein preparations from red- lysogens were tested for ability to promote reannealing, high activity was observed in a mutant altered in the gene for exonuclease, but there was low activity in a mutant altered in the gene for beta protein.