Orientation and sequence analysis of right ends and target sites of bacteriophage mu and D108 insertions in the plasmid pSC101.

We have isolated four independent insertions of the entire 37-kb D108cts 10 genome in the low-copy-number plasmid pSC101 in vivo. They were all formed by replicative transposition during the D108 lytic cycle. The orientation of these four insertions was found to be the same, with the left ends facing towards pSC101 replication, and the right end facing in the direction of all pSC101 transcription, as was previously found for a Mucts62 insertion in pSC101, pMC321. The exact sites of insertion of two of the D108 prophages, as well as the Mu prophage, have been determined by sequence analysis. All three insertions caused a 5-bp duplication of pSC101 sequences at the target site, as has been found for insertions formed by conservative integration upon lysogeny. Moreover, we have determined the nucleotide sequence of the first 75 bp of the right end of D108 and, though this end is interchangeable with the right end of Mu as a substrate for either phage's transposition functions, there are a number of nucleotide differences between them.