Seminars

Two complex machineries contribute to genetic recombination in naturally transformed cells. The first processes drives the transport of DNA into the cytosol, and the second mediates the recombination of the internalized single-stranded (ss) DNA with a homologous resident or with itself for plasmid establishment. In this programmed recombination reaction Bacillus subtilis DprA, RecA, SsbB and SsbA, which are competence-induced, and RecN, RecO, RecU and RecX localize at the DNA entry pole. RecA accessory proteins DprA and RecO acts before and RecF and RecX fater RecA nucleations. SsbA and SsbB bind, protect and melt secondary structures in the ssDNA, and inhibit ssDNA binding by RecA. DprA interacts with SsbB and RecA, and RecO interacts with SsbA. DprA cooperatively binds to ssDNA coated by SsbB protein, and promotes the nucleation of RecA onto SsbB-coated ssDNA, whereas RecO cooperatively binds to ssDNA coated by SsbA protein, and promotes the nucleation of RecA onto SsbA-coated ssDNA. RecX promotes disassembly of a RecA•ssDNA filament and RecF counteracts such effect. The mechanistic framework for rationalizing the coordinated events modulated by SsbA and SsbB and RecF and RecX that are crucial for RecA-dependent chromosomal transformation and RecA-independent plasmid transformation wil be presented.