Biology Reference
In-Depth Information
FIGURE 13.1 Comparison of E. coli T4P biogenesis genes. Arrows indicate genes encoding the
following proteins: red (prepilin); magenta (secretin); dark green (extension ATPase); light green
(retraction ATPase); dark blue (polytopic inner membrane protein); yellow (prepilin peptidase);
light blue (lytic transglycosylase); orange (prepilin-like or minor pilin proteins); purple (bitopic
inner membrane protein); no fill (no corresponding protein in other systems). The arrow depicting
the bfpC gene is half-filled to indicate that the N-terminus of the protein has structural and func-
tional homology to PilM. The slashes indicate that the HCP genes are not contiguous.
Like the bfp operon, the ETEC T4P systems Longus and CFA/III are encoded
by a contiguous operon controlled by a perA -like promoter and found on a very
large plasmid ( Taniguchi et al., 1995, 2001 ; Gomez-Duarte et al., 2007 ). In both
cases, the order of the genes differs substantially from that of the bfp operon,
bearing more similarity to the tcp operon from Vibrio cholerae ( Kirn et al.,
2003 ). Another contiguous operon encodes the R64 conjugative pilus and is
found on the plasmid of the same name ( Kim and Komano, 1997 ; Sakai and
Komano, 2002 ). Here, the genes encoding the putative tip adhesins are orga-
nized in a shufflon located at the end of the operon and the order of the genes
encoding the assembly proteins differs markedly from both the BFP operon and
the Longus/CFA/III operons. The shufflon is comprised of four DNA segments
flanked by inverted repeat sequences. This allows for site-specific recombina-
tion between repeats and the formation of one of seven functional gene prod-
ucts, which have different LPS binding capabilities ( Ishiwa and Komano, 2004 ).
REGULATION
T2S systems are regulated through specific quorum sensing and constitutive
expression mechanisms depending upon the species. Regulation of the ETEC
T2S system is under the control of the yghJ promoter, which is repressed by
global regulatory proteins H-NS and StpA ( Yang et al., 2007 ). It is expected
that these proteins bind directly to the promoter region inhibiting open complex
formation.
Multiple sensory and regulatory systems regulate expression of the BFP. The
pst operon responds to inorganic phosphate starvation and positively regulates
elaboration of the BFP machinery via the per operon ( Ferreira and Spira, 2008 ).
Search WWH ::




Custom Search