title: Contacts between the lac repressor and the thymines in the lac operator.
abstract: We have identified important points of contact between the lac repressor and the lac operator by crosslinking the repressor to bromouracil-substituted operator. We substituted bromouracils for thymines in a 55-base-long restriction fragment containing the lac operator and labeled one or the other 5' end with 32P. Ultraviolet irradiation of this fragment produced single-strand breakds at the bromouracils. We examined breakage at each bromouracil in the sequence by denaturing the DNA and displaying the UV-generated fragments on a polyacrylamide gel. In the presence of lac repressor, UV radiation failed to break at specific sites. We attribute this to a competing reaction in which the DNA crosslinks to the repressor rather than breaking. These crosslinkable sites thus define positions at which the lac repressor protein lies close to the methyl group of a thymine in the major groove of DNA.
mesh_terms: D001483:Base Sequence; D001976:Bromouracil / Q000378:metabolism; D004247:DNA / Q000032:analysis / Q000528:radiation effects; D005796:Genes; D005809:Genes, Regulator; D007785:Lactose / Q000378:metabolism*; D013941:Thymine / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D001976:Bromouracil; D004247:DNA; D007785:Lactose; D013941:Thymine
references.citation: Proc Natl Acad Sci U S A. 1977 Mar;74(3):966-70
references.pmid: 265588
references.citation: Proc Natl Acad Sci U S A. 1977 Feb;74(2):560-4
references.pmid: 265521
references.citation: Nucleic Acids Res. 1977 Mar;4(3):723-37
references.pmid: 866187
references.citation: Proc Natl Acad Sci U S A. 1976 Nov;73(11):4174-8
references.pmid: 1069307
references.citation: Biochemistry. 1973 Jul 31;12(16):3055-63
references.pmid: 4354250
references.citation: J Bacteriol. 1973 Nov;116(2):1064-6
references.pmid: 4583233
references.citation: Q Rev Biophys. 1973 May;6(2):201-46
references.pmid: 4579676
references.citation: Proc Natl Acad Sci U S A. 1973 Dec;70(12):3585-9
references.pmid: 4587256
references.citation: J Biol Chem. 1973 Jan 10;248(1):110-21
references.pmid: 4571224
references.citation: J Mol Biol. 1972 Feb 28;64(1):181-99
references.pmid: 4552482
references.citation: Nucleic Acids Res. 1975 Mar;2(3):383-9
references.pmid: 236548
references.citation: Proc Natl Acad Sci U S A. 1972 Sep;69(9):2574-6
references.pmid: 4560692
references.citation: Cold Spring Harb Symp Quant Biol. 1974;38:247-56
references.pmid: 4524758
references.citation: Proc Natl Acad Sci U S A. 1974 Mar;71(3):947-51
references.pmid: 4522804
references.citation: Anal Biochem. 1974 May;59(1):162-4
references.pmid: 4407732
references.citation: Biochem Biophys Res Commun. 1971 Dec 17;45(6):1542-7
references.pmid: 4942734
references.citation: Biochem J. 1967 Jan;102(1):251-7
references.pmid: 5339944
references.citation: J Mol Biol. 1976 May 5;103(1):25-38
references.pmid: 785008
references.citation: J Bacteriol. 1975 Jan;121(1):354-62
references.pmid: 1090574
references.citation: Nucleic Acids Res. 1976 Jan;3(1):11-8
references.pmid: 1250692
references.citation: Anal Biochem. 1971 May;41(1):51-6
references.pmid: 5578553