The cell pole: the site of cross talk between the DNA uptake and genetic recombination machinery

Abstract

Natural transformation is a programmed mechanism characterized by binding of free double-stranded (ds) DNA from the environment to the cell pole in rod-shaped bacteria. In Bacillus subtilis some competence proteins, which process the dsDNA and translocate single-stranded (ss) DNA into the cytosol, recruit a set of recombination proteins mainly to one of the cell poles. A subset of single-stranded binding proteins, working as “guardians”, protects ssDNA from degradation and limit the RecA recombinase loading. Then, the “mediators” overcome the inhibitory role of guardians, and recruit RecA onto ssDNA. A RecA·ssDNA filament searches for homology on the chromosome and, in a process that is controlled by “modulators”, catalyzes strand invasion with the generation of a displacement loop (D-loop). A D-loop resolvase or “resolver” cleaves this intermediate, limited DNA replication restores missing information and a DNA ligase seals the DNA ends. However, if any step fails, the “rescuers” will repair the broken end to rescue chromosomal transformation. If the ssDNA does not share homology with resident DNA, but it contains information for autonomous replication, guardian and mediator proteins catalyze plasmid establishment after inhibition of RecA. DNA replication and ligation reconstitute the molecule (plasmid transformation). In this review, the interacting network that leads to a cross talk between proteins of the uptake and genetic recombination machinery will be placed into prospective.

Keywords::

• Horizontal gene transfer
• natural competence
• homologous recombination
• chromosomal transformation
• plasmid transformation
• viral transfection

Acknowledgments

We thank B. Carrasco, P. Cardenas and I. Kobayashi for the communication of unpublished results and V. Rodríguez for comments on the manuscript.

Declaration of interest

This work has been supported in part by grants from the Ministerio de Ciencia e Innovación (BFU2009-07167 and CSD2007-00010) to J.C.A and BFU2009-09520 to S.A. DK is supported by NIH/NCI 1 K01 CA15485401A grant. All authors have seen and approved its content. There is no conflict of interest or compelling financial interests.

Editor: Michael M. Cox