Site-specific Recombination by the β Protein from the Streptococcal Plasmid pSM19035: Minimal Recombination Sequences and Crossing over Site

摘要

The β recombinase from the broad host range Gram-positive plasmid pSM19035 catalyzes intramolecular site-specific recombination between two directly or inversely oriented recombination sites in the presence of a chromatin-associated protein (Hbsu). The recombination site had been localized to a 447 bp DNA segment from pSM19035. This segment includes a 90 bp region that contains two adjacent binding sites (I and II) for β protein dimers. Using in vitro recombination assays, we show that this 90 bp region is necessary and sufficient for β protein-mediated recombination; this defines the six site as the region required for β protein binding. The point of crossing over has been localized to the center of site I. Hbsu has a strong binding affinity for an unknown site located within the 447 bp segment containing the six site. We discuss the possibility that Hbsu recognizes an altered DNA structure, rather than a specific sequence, generated in the synaptic complex.