BACTERIOPHAGE-T4 ALC PROTEIN - A TRANSCRIPTION TERMINATION FACTOR SENSING LOCAL MODIFICATION OF DNA

Bacteriophage T4 Alc protein Participates in shutting off host transcr iption after infection of E. coli. It is demonstrated that Alc acts as a site-specific termination factor. The Alc sites occur frequently in E. coli DNA, resulting in early cessation of elongation in several te sted transcription units. Alc-dependent termination requires unimpeded propagation of the elongating complex as it approaches the Alc site. Temporary halting of RNA polymerase within 10-15 bp before the Alc sit e prevents termination. Bacteriophage T4 transcription is protected fr om the action of Alc by overall substitution of cytosine with 5-hydrox ymethyl cytosine in T4 DNA. In vitro methylation of CpG sequences in t he vicinity of an Alc site abolishes the effect of Alc. Thus, Alc-depe ndent termination involves local sensing of the state of cytosine modi fication and a short-term ''memory'' of recent pausing.