THE BACILLUS-SUBTILIS HISTONE-LIKE PROTEIN HBSU IS REQUIRED FOR DNA RESOLUTION AND DNA INVERSION MEDIATED BY THE BETA-RECOMBINASE OF PLASMID PSM19035

The beta recombinase, encoded by the Gram-positive bacterial plasmid p SM19035, is unable to mediate DNA recombination in vitro unless a host factor is provided. The factor has now been identified as the Bacillu s subtilis Hbsu protein. Hbsu is a nonspecific DNA-binding and DNA-ben ding protein. The beta recombinase, in the presence of highly purified Hbsu protein, is able to catalyze in vitro intramolecular recombinati on between two specific recombination sites on a supercoiled DNA molec ule. DNA resolution was obtained when the two crossing over sites (six sites) were directly oriented, whereas DNA inversion was the product when the six sites were in inverse orientation. The ability of the Esc herichia coil chromatin associated proteins HU, IHF, Fis, and H-NS to substitute for Hbsu was investigated. HU efficiently stimulated beta-m ediated recombination, while the effect of IHF was partial and that of Fis and H-NS was undetectable. In addition, the beta protein was able to mediate DNA recombination in both wildtype and IHF-deficient E. co il cells, but failed to do so in an HU-deficient strain. The data pres ented provide direct evidence that a chromatin-associated protein is s trictly required for beta-mediated recombination.