title: Mechanism of action of the cro protein of bacteriophage lambda.
abstract: The mechanism of action of cro protein was probed by measuring its ability to protect DNA against methylation by dimethyl sulfate and its effect on transcription in vitro. The cro protein binds to the same three sites in the right operator (OR) of bacteriophage lambda DNA as does the lambda repressor. Dimethyl sulfate protection experiments reveal major groove contacts for both proteins, and cro protein protects from methylation a subset of those purines protected by lambda repressor. These experiments also show that the relative affinity of these two proteins for the three operator sites is different: whereas lambda repressor binds with an affinity OR1 greater than OR2 greater than OR3, the order for cro protein is OR3 greater than (OR1, OR2). As predicted by these results, cro protein, like the lambda repressor, blocks in vitro transcription of cI and cro from the two divergent promoters that overlap OR. Also as predicted, transcription of cI is turned off at lower cro protein concentrations than is transcription of cro, whereas the opposite order of repression is obtained with lambda repressor. These results describe the molecular mechanism of cro protein action and show that two regulatory proteins can bind to the same three adjacent sites in DNA with markedly different consequences.
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D003090:Coliphages / Q000235:genetics / Q000502:physiology*; D004279:DNA, Viral / Q000378:metabolism; D005809:Genes, Regulator; D005814:Genes, Viral; D014158:Transcription, Genetic; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*
chemical_list: D004279:DNA, Viral; D014764:Viral Proteins
references.citation: J Biol Chem. 1977 Sep 10;252(17):6177-83
references.pmid: 330523
references.citation: Proc Natl Acad Sci U S A. 1977 Feb;74(2):560-4
references.pmid: 265521
references.citation: Nature. 1977 Nov 17;270(5634):275-7
references.pmid: 593348
references.citation: Nature. 1977 Nov 17;270(5634):274-5
references.pmid: 593347
references.citation: Nucleic Acids Res. 1977;4(5):1595-607
references.pmid: 896470
references.citation: Proc Natl Acad Sci U S A. 1976 Nov;73(11):4174-8
references.pmid: 1069307
references.citation: Proc Natl Acad Sci U S A. 1976 Feb;73(2):293-7
references.pmid: 1061131
references.citation: Proc Natl Acad Sci U S A. 1975 Mar;72(3):1184-8
references.pmid: 1055375
references.citation: Science. 1976 Oct 8;194(4261):156-61
references.pmid: 959843
references.citation: Cell. 1975 Jun;5(2):109-13
references.pmid: 1095210
references.citation: Virology. 1974 Nov;62(1):224-33
references.pmid: 4609081
references.citation: J Mol Biol. 1973 Oct 25;80(2):203-16
references.pmid: 4587402
references.citation: Proc Natl Acad Sci U S A. 1973 Dec;70(12):3585-9
references.pmid: 4587256
references.citation: Annu Rev Genet. 1973;7:289-324
references.pmid: 4593306
references.citation: Mol Biol Rep. 1974 Sep;1(7):385-90
references.pmid: 4472898
references.citation: Proc Natl Acad Sci U S A. 1976 Jul;73(7):2249-53
references.pmid: 1065873
references.citation: Proc Natl Acad Sci U S A. 1975 Dec;72(12):4785-89
references.pmid: 1061069