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Activator‐independent formation of a closed complex between σ 54 ‐holoenzyme and nifH and nifU promoters of Klebsiella pneumoniae
Author(s) -
Buck Martin,
Can Wendy
Publication year - 1992
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1992.tb00887.x
Subject(s) - promoter , biology , sigma factor , klebsiella pneumoniae , rna polymerase , activator (genetics) , gene , genetics , nitrogen fixation , nitrogenase , specificity factor , transcription (linguistics) , dna , microbiology and biotechnology , rna , escherichia coli , gene expression , bacteria , linguistics , philosophy
Summary The alterNatlve sigma factor σ 54 is required for transcription of nitrogen fixation genes in Klebsiella pneutnoniae and other diazotrophs. The nif genes, and other Eσ 54 ‐dependent genes whose products are necessary for a wide range of processes, are positively regulated. A unifying model that is well supported by studies on nif and other nitrogen‐regulated (ntr) genes includes the central tenet that σ 54 confers upon core RNA polymerase the ability to recognize and bind specific promoter sequences, but not the ability to isomerize to the open complex without assistance from the appropriate activator protein. Direct physical evidence for formation of an activator‐independent complex between Eσ 54 and the NifA‐dependent K. pneumoniae nifH and nifU promoters has, to date, been lacking. Using purified components we have now demonstrated formation of the closed complex at these promoters, indicating that it is an intermediate along the pathway to open complex formation. The closed complex was not detected when conserved features of the promoter were altered by mutation, nor was its stability increased when integration host factor protein was bound adjacent to the Eσ 54 recognition sequence.