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Differential regulation of multiple overlapping promoters in flagellar class II operons in Escherichia coli
Author(s) -
Liu Xiaoying,
Matsumura Philip
Publication year - 1996
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.1365-2958.1996.tb02569.x
Subject(s) - operon , rna polymerase , sigma factor , biology , promoter , transcription (linguistics) , gene , escherichia coli , genetics , gene expression , linguistics , philosophy
Summary The Escherichia coli flagellar operons are divided into three categories: classes I, II and III. Expression of class II depends on expression of class I. One of the class II gene products, the FliA protein, is an alternative ß factor (ß 28 ) required for transcription of the class III operons. In this study, we have characterized, in vitro , a role of ß 28 in the regulation of the class II operons. Among the three class II operons examined, the fliA and fliL operons, but not the flhB operon, could be transcribed by both ß 70 RNA polymerase holoenzyme with FlhD/C (Eß 70 ‐FlhD/C) and ß 28 RNA polymerase holoenzyme (Eß 28 ). The flhB operon could only be transcribed by Eß 70 ‐FlhD/C under the conditions used. Both the fliA and fliL operons contained two overlapping promoters oriented in tandem. The transcription of fliA directed by Eß 28 could outcompete that by Eß 70 ‐FlhD/C, indicating a positive autoregulation. However, Eß 28 could not displace Eß 70 ‐FlhD/C bound to the fliL promoter. The c 28 ‐mediated positive regulation of the class II operons involved a mechanism in which ß 28 competed with ß 70 for core RNA polymerase. In addition, recruitment of core RNA polymerase from the ß 70 ‐10 site to the ß 28 ‐10 was facilitated by formation of Eß 70 ‐FlhD/C pre‐initiation complex. Taken together, the three class II promoters investigated are different in terms of their regulation by ß 28 . We propose that class II operons may be further divided into different subcategories.