HOMOLOGOUS PAIRING PROTEINS ENCODED BY THE ESCHERICHIA-COLI RECE AND RECT GENES

Early genetic analysis of alternate recombination pathways in Escherichia coli identified the RecE recombination pathway and the required exonuclease VIII encoded by the recE gene. Observations that not all recombination events promoted by the RecE pathway require recA suggest the existence of an additional homologous pairing protein besides RecA in E. coli. Genetic and biochemical analysis of the recE gene region indicates there are two partially overlapping genes, recE and recT, encoding at least two proteins: exoVIII and the RecT protein. Biochemical analysis has shown that the RecT protein, in combination with exoVIII, promotes homologous pairing and strand exchange in reactions containing linear duplex DNA and homologous, circular, single-stranded DNA as substrates. This reaction occurs in the absence of any high-energy cofactor. These two proteins, RecT and exoVIII, appear to be members of a second class of homologous pairing proteins that are required in genetic recombination and differ from the class of homologous pairing proteins that includes RecA. Members of this second class of proteins appear to include both bacteriophage-encoded proteins and proteins from eukaryotes and their viruses.