Illegitimate recombination in Bacillus subtilis: a site-specific mechanism in the formation of plasmid pKBT1

The Bacillus subtilis plasmid pKBT1, the product of in vivo recE4-independent recombinal events, contains segments derived from pUB110 and the B. subtilis chromosome. To determine whether the pUB110 sequence is intact in PKBT1, two 1 kb fragments, each containing a site at which chromosomal and pUB110 sequences are joined, were cloned and sequenced. Sequencing data revealed that: 1). An intact copy of pUB110 is present in pKBT1; 2) The apparent recombination sites were adjacent to the Bam HI-generated ends of pUB110 sequences; 3) pTL12-derived sequences from the original transforming DNA were limited to no more than 1 bp outside the Bgl II recognition sequence; 4) Recombination sites at both ends of pUB110 contain a 19 bp inverted repeat with 15 homologous nucleotides. These findings suggest a site-specific mechanism acting during in vivo formation of pKBT1.