TRANSCRIPTION OF A BACTERIOPHAGE-LAMBDA DNA SITE BLOCKS GROWTH OF ESCHERICHIA-COLI

The rap mutation in Escherichia coli prevents the growth of bacterophage λ. Phage mutations that overcome rap inhibition (bar) have been mapped to loci in the p(L) operon. We cloned and sequenced three mutations in two of these loci: barIa to the left arm of the λ attachment site (attP) and barII in the ssb (ea10) gene). The mutations represent single base-pair changes within nearly identical 16-base-pair DNA segments. Each mutation disrupts a sequence of dyad symmetry within the segment. Plasmids carrying a bar+ sequence downstream to an active promoter are lethal to rap, but not rap+, bacteria. The bar sequences isolated from the λ bar mutants are not lethal. We synthesized a minimal λ barIa+ sequence, 5'-TATATTGATATTTATATCATT, and cloned it downstream to an inducible promoter. When transcribed, this sequence is sufficient to kill a rap strain.