Insertions, deletions and mismatches in heteroduplex DNA made by recA protein.

E. coli recA protein promotes the pairing of circular single strands with linear duplex DNA and the subsequent formation of large heteroduplex joints. From fd and M13 DNA, recA protein can make heteroduplex joints that include every kind of single base-pair mismatch. Aided by E. coli single-strand binding protein (SSB) and ATP regeneration, recA protein can incorporate into heteroduplex DNA insertions that are hundreds of base pairs long, whether the extra DNA is located initially in either the single-stranded or the double-stranded substrate. The ability of recA protein to span large insertions in the duplex DNA indicates that it unwinds a sizeable number of turns in advance of the growing heteroduplex joint. These observations show that an enzymatic basis exists in E. coli for forming extensively mismatched heteroduplex DNA, which might be involved in conversion-like events associated with recombination.