THE SITE-SPECIFIC INTEGRATION SYSTEM OF THE TEMPERATE STREPTOCOCCUS-THERMOPHILUS BACTERIOPHAGE-PHI-SFI21

The temperate bacteriophage phi Sfi21 integrates its DNA into the chro mosome of Streptococcus thermophilus strains via site-specific recombi nation. Nucleotide sequencing of the attachment sites identified a 40- bp identity region which surprisingly overlaps both the 18-terminal bp of the phage integrase gene and the 11-terminal bp of a host tRNA(Arg ) gene. A 2.4-kb phage DNA segment, covering attP, the phage integrase , and a likely immunity gene contained all the genetic information for faithful integration of a nonreplicative plasmid into the attB site. A deletion within the int gene led to the loss of integration proficie ncy A number of spontaneous deletions were observed in plasmids contai ning the 2.4-kb phage DNA segment. The deletion sites were localized t o the tRNA side of the identity region and to phage or vector DNA with 3- to 6-bp-long repeats from the border region. A similar type of del etion was previously observed in a spontaneous phage mutant. (C) 1997 Academic Press.