Regulation of Mu transposition. I. Localization of the presumed recognition sites for HimD and Ner functions controlling bacteriophage Mu transcription.

The Escherichia coli HimD function (also known as Hip) is essential for Mu development (Miller and Friedman, 1977). We show that the role of HimD is to stimulate early transcription of Mu DNA, probably by acting as a subunit of integration host factor (IHF) and binding at a site located approx. 70 bp upstream from the start of the early transcription. HimD-independent phages were isolated. These mutant phages carry a promoter-up mutation in the Pribnow-box of the early promoter. Early Mu transcription is negatively regulated by the repressor (c gene product) and the Ner proteins. Mutants were isolated which are insensitive to the overproduction of Ner by multicopy plasmids, which normally inhibits Mu development. The mutations that map close to the startpoint of the early transcription reveal a structure which is presumably the Ner recognition site.