Transposition of λp lacMu is mediated by the A protein altered at its carboxy-terminal end

Abstract

λp lacMu phages are derivatives of bacteriophage λ that use the transposition machinery of phage Mu to insert into chromosomal and cloned genes. When inserted in the proper fashion, these phages yield stable fusions to the Escherichia coli lac operon in a single step. We have determined the amount of DNA from the c end of phage Mu present in one of these phages, λp lacMu3, and have shown that this phage carries a 3137-bp fragment of Mu DNA. This DNA segment carries the Mu c-end attachment site and encodes the Mu genes cts62, ner + , and gene A lacking 179 bp at its 3′ end ( A′). The product of this truncated gene A′ retains transposase activity and is sufficient for the transposition of λp lacMu. This was demonstrated by showing that λp lacMu derivatives carrying the A am1093 mutation in the A′ gene are unable to transpose by themselves in a Su − strain, but their transposition can be triggered by coinfection with λpMu507( A + B + ). We have constructed several new λp lacMu phages that carry the A′ am1093 gene and the kan gene, which confers resistance to kanamycin. Chromosomal insertions of these new phages are even more stable than those of the previously reported λp lacMu phages, which makes them useful tools for genetic analysis.