Sigma Competition: The Contest between Bacteriophage T4 Middle and Late Transcription

• Published in: Journal of molecular biology 1999-08, Vol.291 (2), p.267-281
• Main Authors: Kolesky, Scott, Ouhammouch, Mohamed, Brody, Edward N., Geiduschek, E.Peter
• Format: Article
• Language: English
• Subjects: Animals; anti-sigma; bacteriophage T4; Bacteriophage T4 - genetics; DNA-Binding Proteins - metabolism; DNA-Directed RNA Polymerases - metabolism; holoenzyme competition; Osmolar Concentration; Phage T4; Promoter Regions, Genetic; Rabbits; Sigma Factor - metabolism; sliding clamps; Templates, Genetic; Trans-Activators - metabolism; Transcription Factors - metabolism; Transcription, Genetic; Transcriptional Activation; transcriptional regulation; Viral Proteins - metabolism
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1006/jmbi.1999.2953

In bacterial transcription, diverse σ-family promoter recognition proteins compete for a common RNA polymerase core. Bacteriophage T4 infection ultimately reduces this competition to a duel between activated viral middle and enhanced late transcription, involving two σ proteins, two phage-encoded activator proteins and two phage-specific co-activators. This competition has been analyzed in vitro, and the relative abundances in T4-infected Escherichia coli of the participating proteins have been measured. Activated late transcription holds an advantage over activated middle transcription, especially at higher ionic strength. This advantage is further compounded by ADP-ribosylation of the RNA polymerase α subunits, and by the phage-specific, RNA polymerase core-bound RpbA subunit. The largest contribution to the middle-late competition is made by gp55, the late σ factor, but not enough of gp55 is produced during T4 infection to shut off middle transcription by direct competition with σ 70. AsiA, the originally identified anti-σ protein is not a major determinant of middle-late competition.