title: LeuO-mediated transcriptional derepression.
abstract: To understand the coordination of gene expression in the Salmonella typhimurium ilvIH-leuO-leuABCD gene cluster, we had previously identified a 72-bp AT-rich (78% A+T) DNA sequence element, AT4, which was capable of silencing transcription in a promoter nonspecific manner. LeuO protein provided in trans relieved (derepressed) AT4-mediated gene silencing (transcriptional repression), but underlying mechanisms remained unclear. In the present communication, the 72-bp DNA sequence element is further dissected into two functional elements, AT7 and AT8. LeuO binds to the 25-bp AT7, which lies closest to the leuO promoter in the AT4 DNA. After deletion of the AT7 DNA sequence responsible for LeuO binding from AT4, the remaining 47-bp AT-rich (85% A+T) DNA sequence, termed AT8, retains the full bi-directional gene-silencing activity, which is no longer relieved by LeuO. LeuO-mediated transcriptional derepression is restored when the LeuO binding site, AT7, is placed within close proximity to the gene silencer AT8. As a pair of functionally coupled transcription elements, the presence of an equal copy number of AT7 and AT8 within proximity is important for the transcription control. The characterization provides clues for future elucidation of the molecular details whereby LeuO negates the gene-silencing activity.
authors.affiliation: Department of Pharmacology, School of Medicine, Wayne State University, Detroit, Michigan 48201, USA.
authors.forename: Chien-Chung
authors.initials: CC
authors.lastname: Chen
authors.forename: Mugdha
authors.initials: M
authors.lastname: Ghole
authors.forename: Arundhati
authors.initials: A
authors.lastname: Majumder
authors.forename: Zhijian
authors.initials: Z
authors.lastname: Wang
authors.forename: Sreenivasa
authors.initials: S
authors.lastname: Chandana
authors.forename: Hai-Young
authors.initials: HY
authors.lastname: Wu
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D029968:Escherichia coli Proteins; D020868:Gene Silencing; D008969:Molecular Sequence Data; D010957:Plasmids; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic
chemical_list: D029968:Escherichia coli Proteins; C430340:LeuO protein, E coli; D014157:Transcription Factors