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Titolo:
Dimeric lac repressors exhibit phase-dependent co-operativity
Autore:
Muller, J; Barker, A; Oehler, S; Muller-Hill, B;
Indirizzi:
Univ Cologne, Inst Genet, D-50931 Cologne, Germany Univ Cologne Cologne Germany D-50931 nst Genet, D-50931 Cologne, Germany
Titolo Testata:
JOURNAL OF MOLECULAR BIOLOGY
fascicolo: 4, volume: 284, anno: 1998,
pagine: 851 - 857
SICI:
0022-2836(199812)284:4<851:DLREPC>2.0.ZU;2-T
Fonte:
ISI
Lingua:
ENG
Soggetto:
ESCHERICHIA-COLI; COOPERATIVE BINDING; PHYSICAL-PROPERTIES; CRYSTAL-STRUCTURE; LAMBDA-REPRESSOR; GAL REPRESSOR; DNA INVIVO; OPERATOR; OPERON; TRANSCRIPTION;
Keywords:
protein-DNA recognition; DNA looping; DNA helical repeat; Lac repressor; Gal repressor;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Life Sciences
Citazioni:
43
Recensione:
Indirizzi per estratti:
Indirizzo: Muller-Hill, B Univ Cologne, Inst Genet, Weyertal 121, D-50931 Cologne, Germany Univ Cologne Weyertal 121 Cologne Germany D-50931 Germany
Citazione:
J. Muller et al., "Dimeric lac repressors exhibit phase-dependent co-operativity", J MOL BIOL, 284(4), 1998, pp. 851-857

Abstract

Transcription of the lac operon in Escherichia coli is repressed by the binding of Lac repressor (LacR) to lac operator O-1, a pseudo-palindromic sequence centred 11 bp downstream of the transcription start. Full repression of the wild-type promoter by wild-type, tetrameric LacR requires the presence of at least two operator sequences that must not only be in close proximity to O-1, 401 bp and 92 bp for the auxiliary operators O-2, and O-3, respectively, but must also be present on the same side of the DNA helix. LacR mutants lacking the C-terminal heptad repeat and thus only capable of dimerformation still repress, but at a much reduced level. Their repression of the inc promoter is comparable to repression by tetrameric LacR when both auxiliary operators are destroyed. We have examined the residual repression,by dimeric LacR, of a series of constructs containing a CAP-independent promoter and two lac operators, O-1, and O-id, separated by a series of spacers increasing in size by single base-pair increments. Surprisingly, repression of these constructs still exhibits phase dependence. The periodicity ofmaxima is similar to the helical repeat of DNA in vivo, as measured by phase-dependent repression with tetrameric LacR, although the magnitude of repression is much smaller than that obtained in previous experiments with tetrameric LacR. Two additional variants of dimeric LacR with altered C termini that were tested also show phase dependence. Control experiments show that the presence of O-1, is required for repression in this system. In the absence of O-1, occupancy of the auxiliary operator does not lead to repression. The magnitudes of repression maxima correlate best with the overall basic nature of the C terminus. Weak, unspecific contacts by this region with DNA seem sufficient to explain the observed periodicity. It remains to be seen wether additional factors are also involved in this residual repression. (C) 1998 Academic Press.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 21/09/20 alle ore 16:13:53