recA protein-promoted DNA strand exchange. Effect of ionic strength

The addition of from 80 to 120 mM NaCl to a recA protein-promoted DNA strand exchange results in a significant increase in both the initial rate and extent of reaction. This increase results from the formation of a relatively stable recA protein-single-stranded DNA complex that is similar to the complex formed in the presence of the single-stranded DNA-binding protein. In addition to increasing the rate and extent of strand exchange, the amount of recA protein and ATP hydrolysis needed to promote these reactions efficiently is reduced. However, single-stranded DNA-binding protein is significantly more effective than addition of 100 mM NaCl in promoting stable complex formation and stimulating strand exchange. These findings support the hypothesis that a stable recA protein-single-stranded DNA complex is required for efficient DNA strand exchange.