title: Sequence changes in coliphage lambda mutants affecting the nutL antitermination site and termination by tL1 and tL2.
abstract: The 17-bp sequence designated nutL is required for the N-mediated antitermination of transcription in the major leftward operon of coliphage lambda. The single-stranded sequence can be folded into a hairpin structure. Ten independently isolated spontaneous lambda nutL- mutants have changes that affect the same nucleotide, located in the loop of the hairpin structure, changing the guanine to adenine, thymine or cytosine. Another mutant (lambda nutL3), selected by a different means, has a deletion of one GC base pair and thus eliminates one C in the stem of the hairpin structure, destabilizing it -11.2 to -2.2 kcal/mol. True reversions of the nutL point mutations restore the guanine. The second-site revertant lambda ninL99 was found to have a deletion of 417 bp between the tL1 terminator and the N gene, removing bases +523 to +939 (counted from SL = +1). This deletion include codons for the six carboxy-terminal amino acids of gene N product, but the fusion allows continuation of translation for 53 additional amino acid residues beyond the truncated N gene before reaching a nonsense codon. The fused N product is active.
mesh_terms: D010582:Bacteriophage lambda / Q000235:genetics*; D001483:Base Sequence; D004279:DNA, Viral / Q000235:genetics; D005786:Gene Expression Regulation; D005809:Genes, Regulator; D005814:Genes, Viral; D009154:Mutation; D012367:RNA, Viral / Q000235:genetics; D014158:Transcription, Genetic; D014764:Viral Proteins / Q000235:genetics
chemical_list: D004279:DNA, Viral; D012367:RNA, Viral; D014764:Viral Proteins