title: A 72-base pair AT-rich DNA sequence element functions as a bacterial gene silencer.
abstract: We have previously demonstrated that sequential activation of the bacterial ilvIH-leuO-leuABCD gene cluster involves a promoter-relay mechanism. In the current study, we show that the final activation of the leuABCD operon is through a transcriptional derepression mechanism. The leuABCD operon is transcriptionally repressed by the presence of a 318-base pair AT-rich upstream element. LeuO is required for derepressing the repressed leuABCD operon. Deletion analysis of the repressive effect of the 318-bp element has led to the identification of a 72-bp AT-rich (78% A+T) DNA sequence element, AT4, which is capable of silencing a number of unrelated promoters in addition to the leuABCD promoter. AT4-mediated gene silencing is orientation-independent and occurs within a distance of 300 base pairs. Furthermore, an increased gene-silencing effect was observed with a tandemly repeated AT4 dimer. The possible mechanism of AT4-mediated gene silencing in bacteria is discussed.
authors: Department of Pharmacology, School of Medicine, Wayne State University, Detroit, Michigan 48201, USA.
authors: C C
authors: CC
authors: Chen
authors: M
authors: M
authors: Fang
authors: A
authors: A
authors: Majumder
authors: H Y
authors: HY
authors: Wu
mesh_terms: D020029:Base Pairing; D001483:Base Sequence; D017931:DNA Primers; D004269:DNA, Bacterial / Q000235:genetics*; D020868:Gene Silencing; D008969:Molecular Sequence Data; D009876:Operon; D011401:Promoter Regions, Genetic; D012486:Salmonella typhimurium / Q000235:genetics*
chemical_list: D017931:DNA Primers; D004269:DNA, Bacterial