In most prokaryotes, cell division
is accomplished by a multiprotein complex, called the
divisome. The scaffold for assembling the divisome is
provided by the Z-ring, which is a ring-like structure that
forms during polymerization of FtsZ molecules at midcell.
Coordination of Z-ring formation as well as divisome assembly
and stability are crucial for successful proliferation.
Several factors that stabilize the division apparatus have
been characterized. However, these factors appear to be
phylogenetically unrelated and to fulfill a rather
species-specific function during cell division. This raises
the question of what additional factors are required to
ensure efficient cell division in C. crescentus. Here, I
report the identification of the novel cell division protein
CedX (cell division protein X). CedX is a proline-rich inner
membrane protein that localizes in an FtsZ- and FtsN-
dependent manner to the cell division plane. Interestingly,
it was found that overproduction of CedX blocks cell division
and causes the formation of several non-contractile Z-rings.
Functional analysis of CedX mutant derivatives demonstrated
that CedX requires its membrane anchor and proline-rich
region for proper localization and protein-protein
interaction. In addition, coimmunoprecipation and bacterial
two-hybrid analyses suggest that CedX not only interacts with
FtsZ and FtsN but also with several other late cell division
proteins. Colocalization experiments with fluorescently
tagged derivatives of FtsZ, FtsA, FtsN and CedX further
support the notion that CedX is a late recruit to the cell
division apparatus. However, it remains to be elucidated
under which conditions CedX becomes essential for proper cell
division. Collectively, these findings suggest that CedX is
an accessory divisome component that presumably supports the
assembly process of late divisome components by means of its
unstructured proline-rich C-terminal tail. Apart from cell
division, the formation of a prostheca, also known as stalk,
is another characteristic change in cell morphology, which is
a widespread phenomenon among bacteria and also an obligatory
developmental checkpoint in the C. crescentus life cycle. In
C. crescentus, the stalk represents a thin extension of the
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