title: Bacteriophage P22 antitermination boxB sequence requirements are complex and overlap with those of lambda.
abstract: Transcription antitermination in phages lambda and P22 uses N proteins that bind to similar boxB RNA hairpins in regulated transcripts. In contrast to the lambda N-boxB interaction, the P22 N-boxB interaction has not been extensively studied. A nuclear magnetic resonance structure of the P22 N peptide boxB(left) complex and limited mutagenesis have been reported but do not reveal a consensus sequence for boxB. We have used a plasmid-based antitermination system to screen boxBs with random loops and to test boxB mutants. We find that P22 N requires boxB to have a GNRA-like loop with no simple requirements on the remaining sequences in the loop or stem. U:A or A:U base pairs are strongly preferred adjacent to the loop and appear to modulate N binding in cooperation with the loop and distal stem. A few GNRA-like hexaloops have moderate activity. Some boxB mutants bind P22 and lambda N, indicating that the requirements imposed on boxB by P22 N overlap those imposed by lambda N. Point mutations can dramatically alter boxB specificity between P22 and lambda N. A boxB specific for P22 N can be mutated to lambda N specificity by a series of single mutations via a bifunctional intermediate, as predicted by neutral theories of evolution.
authors.affiliation: Department of Biology, American University of Beirut, Riad El Solh 1107 2020, Beirut, Lebanon.
authors.forename: Alexis I
authors.initials: AI
authors.lastname: Cocozaki
authors.forename: Ingrid R
authors.initials: IR
authors.lastname: Ghattas
authors.forename: Colin A
authors.initials: CA
authors.lastname: Smith
mesh_terms: D017100:Bacteriophage P22 / Q000235:genetics* / Q000378:metabolism; D010582:Bacteriophage lambda / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D005814:Genes, Viral / Q000235:genetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017354:Point Mutation; D012367:RNA, Viral / Q000235:genetics; D014158:Transcription, Genetic; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D012367:RNA, Viral; D014764:Viral Proteins