Nucleic Acids Research, 2008, Vol. 36, No. 1 119 Figure 6. Mode of action of RecN protein: a proposal. RecN binds ssDNA regions of broken DNA molecule (e.g. a single-strand nick in the lagging strand template) (A). In the presence of ATP–Mg2+ and prior DNA end-processing, RecN binds to the 30-end of ssDNA tailed duplex DNA, because it binds with high eﬃciency to short ssDNA segments, whereas SsbA requires patches of ssDNA longer than 35-nt. The 50 ends of the broken DNA molecules are processed either by RecJ in concerts with a RecQ-like protein (namely RecQ or RecS) or the AddAB helicase/nuclease, resulting in a duplex molecule with a 30-terminated ssDNA tail (B). After end-processing, RecN by a protein–protein and protein–ssDNA interaction forms 1 to 2 RecN foci in vivo and large nucleoprotein networks (rosette-like structures) in vitro, and SsbA binds and protects the ssDNA (C). RecN and RecA interaction leads to disassembly of the rosette-like structures. In the absence of SsbA, RecN helps loading RecA onto naked ssDNA and RecA polymerizes onto ssDNA to form the active RecA nucleoprotein ﬁlament formation (D). In vivo RecN directly or indirectly interacts with RecO (and perhaps RecR), and the RecA-mediators might promote the disassembly of the SsbA protein and the loading of RecA onto ssDNA. The role of the RecA-mediators remains to be unravelled. ACKNOWLEDGEMENTS We are very grateful to R.L. Ohniwa for valuable discussions on this work, and to L.B. Rothman-Denes, J. Reeve and C. Wyman for comments on the article. H.S. was recipient of a Fellowship of the Spanish Research Council and the Japanese Society for the Promotion of Science. This work was supported by grants BFU2006-01062 and CSD2007-00010 from Ministerio de Educacio´ n y Ciencias to J.C.A., S-0505/- MAT0283 from Comunidad de Madrid, and Grant-in-aid for Priority Area from the MEXT of Japan to K.T. Funding to pay the Open Access publication charges for this article was provided by BFU2006-01062 grant. Conﬂict of interest statement. None declared.