Mutations reducing the activity of c17, a promoter of phage lambda formed by a tandem duplication.

We report the isolation of four independently selected mutations (scs) in the c17 promoter of phage lambda that reduce or eliminate the promoter activity. The c17 promoter is not normally present in lambda, and has been shown to be generated by a tandem duplication which creates a "Pribnow Box," a heptamer sequence implicated in promoter activity. This sequence is located upstream from the site of transcription initiation and is present, with some variation, in all promoters whose sequences have been determined. Analysis of the c17 duplications carrying the scs mutations reveals that three of these mutants carry single base-pair changes in the most highly conserved base pairs of the Pribnow Box and that the other mutation is a reversion to the wild type sequence in this region (i.e., a loss of the duplicated base pairs).