THE SRE GENE (ORF469) ENCODES A SITE-SPECIFIC RECOMBINASE RESPONSIBLEFOR INTEGRATION OF THE R4 PHAGE GENOME

The sre gene (ORF469) of the R4 phage encodes a protein similar to the resolvase-DNA invertase family proteins. Insertional gene disruption of sre prevented a lysogen from entering the lytic cycle, implying tha t Sre protein is a site-specific recombinase needed for excision of th e R 4 prophage genome (M. Matsuura, T. Noguchi, T. Aida, M. Asayama, H . Takahashi, and M. Shirai, J. Gen, Appl, Microbiol, 41:53-61, 1995). To determine whether this sre gene is also necessary for the integrati on reaction, we studied its function by integration plasmid analysis. When deletions, frameshifts, and site directed mutations that caused a n amino acid substitution of Ser-17 for Ala were introduced into the s re structural gene, transformation effciency of Streptogyces parvulus 2297 with these plasmid DNAs was severely reduced. However, an adenine insertion just before the possible initiation codon of the sre gene d id not significantly decrease the efficiency. These data suggest that the Sre protein is a site-specific recombinase responsible for integra tion of the R4 phage genome.