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OPAC HELP

Titolo:
NAG REPRESSOR-OPERATOR INTERACTIONS - PROTEIN-DNA CONTACTS COVER MORETHAN 2 TURNS OF THE DNA HELIX
Autore:
PLUMBRIDGE J; KOLB A;
Indirizzi:
INST BIOL PHYS CHIM,URA 1139,13 RUE PIERRE & MARIE CURIE F-75005 PARIS FRANCE INST PASTEUR,URA 1149 F-75015 PARIS FRANCE
Titolo Testata:
Journal of Molecular Biology
fascicolo: 5, volume: 249, anno: 1995,
pagine: 890 - 902
SICI:
0022-2836(1995)249:5<890:NRI-PC>2.0.ZU;2-L
Fonte:
ISI
Lingua:
ENG
Soggetto:
ESCHERICHIA-COLI K-12; LAC REPRESSOR; NUCLEOTIDE-SEQUENCE; TRANSCRIPTIONAL ANALYSIS; RECOGNITION HELIX; CRYSTAL-STRUCTURE; CYTR REPRESSOR; GAL OPERON; BINDING; COMPLEX;
Keywords:
PROTEIN-DNA RECOGNITION; NAGE-B OPERATOR; NAGC REPRESSOR; CAMP/CAP;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
53
Recensione:
Indirizzi per estratti:
Citazione:
J. Plumbridge e A. Kolb, "NAG REPRESSOR-OPERATOR INTERACTIONS - PROTEIN-DNA CONTACTS COVER MORETHAN 2 TURNS OF THE DNA HELIX", Journal of Molecular Biology, 249(5), 1995, pp. 890-902

Abstract

The NagC repressor binds to two sites in the intergenic nagE-B regionoverlapping the divergently expressed nagE and nagB promoters. In addition the NagC repressor binds to two sites upstream of the manXYZ operon. Although basically palindromic, there is little sequence consensus between the four operators. To identify the DNA sequence important for NagC recognition, we have taken advantage of the fact that repression of the nagE and nagB genes requires the formation of a loop of DNA between molecules of the repressor bound to the nagE and nagB operators. The nagE operator was systematically mutagenised and the effect of the mutations measured on the level of expression from a nagB-lacZ fusion. These experiments showed that the most important positions for recognition are the two AT base-pairs at positions -5 and -6 from the centre of symmetry These are the only absolutely conserved bases in the four operators. Certain changes of residues at position -3 and -4 havefairly strong effects while changes at -7 to -10 have only minor effects. However the presence of a G or C base at positions +11 or -11 produces a NagC binding site with considerably higher affinity than the wide-type nagE operator both in vitro and in vivo, a ''super-operator''. The presence of a super-operator considerably increased the stability of the binary looped NagC-DNA complex in vitro. However in the presence of cAMP/CAP, NagC showed the same apparent binding affinity to wild-type and super-operators indicating that one role of cAMP/CAP in therepression complex is to reduce the need for high affinity sites. These super-operators allow a higher level of repression of the nagE promoter compared to the nagB, presumably due to the existence of linear complexes of NagC bound to BoxE.

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Documento generato il 20/09/20 alle ore 00:25:08