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J. Bacteriol., 06 1996, 3544-3549, Vol 178, No. 12
O Francetic and AP Pugsley
Systematic sequencing of the Escherichia coli K-12 chromosome (GenBank
entry U18997) has revealed the presence of an apparently complete operon of
genes (the gspC-0 operon) similar to genes coding for components of the
main terminal branch of the general secretory pathway (e.g., the Klebsiella
oxytoca pulC-0 pullulanase secretion operon) and to related genes required
for type IV pilus biogenesis. For example, the last gene in the gsp operon,
gspO (formerly hopD), encodes a protein which is similar to several type IV
prepilin peptidases. Expression of gspO from lacZp promotes cleavage of two
known prepilin peptidase substrates in E. coli K-12: Neisseria gonorrhoeae
type IV prepilin and K. oxytoca prePulG protein. gspO also complements a
mutation in the corresponding gene (pulO) of the pullulanase secretion
operon when it is expressed from lacZp. Another gene in the gsp operon,
gspG (formerly hopG), encodes a protein similar to prePulG, a component of
the pullulanase secretion pathway. Expression of gspG from lacZp leads to
production of a protein which (i) is recognized by PulG- specific antiserum
(and by antiserum against the Pseudomonas aeruginosa PulG homolog XcpG
[formerly XcpT]), (ii) is processed in cells expressing gspO, and (iii)
restores secretion in cells carrying a pulG mutation. The chromosomal
copies of gspG and gspO are apparently not expressed, probably because of
very weak transcription from the upstream region, as measured by using a
chromosomal gspC-lacZ operon fusion. Thus, the gsp operon of E. coli K-12
includes at least two functional genes which, together with the rest of the
operon, are probably not expressed under laboratory conditions.
Copyright © 1996, American Society for Microbiology
The cryptic general secretory pathway (gsp) operon of Escherichia coli K-12 encodes functional proteins
Unite de Genetique Moleculaire, Centre National de la Recherche Scientifique Unite de Recherche Associee 1149, Institut Pasteur, Paris, France.
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