On to
Caulobacter!
0.7 um in diameter
2-3 um long
Swarmer cell
Stalk cell
The stalked bacterium
Graphical
4,016,942 bp
Representations
of the
3767 ORFs
(CW and CCW)
Genome
A Sticky
Wicket
Wild-type Vibriod Cells
Elongated stationary phase cells
Transposon Insertion
Complementation by Normal Gene
2 um
Shaping a CrescentShaped Cell: Crescentin
Cresecentin
Filaments
Shape
Caulobacter
optical sections of stationary phase cells
Crescentin is
an
Intermediate
Filament
Ortholog
MreB Directs
Wall Synthesis
as in E. coli
Xylose-regulatable MreB Turned Off
After Switch to Xylose-Free Medium
Depletion and
Overexpression
Both Disturb
Partitioning
MreB Also
Positions the
Chromosomes
40/60
split
And FtsZ is Involved in Division
xylose medium
glucose medium
Xylose-regulatable FtsZ
complementation
by a wild-type ftsZ allele
Prokaryotes Contain Orthologs of All Three Major
Filamentous Networks of the Eukaryotic Cytoskeleton
EM scale bars 100nm
Light microscope bars 2 um
The Caulobacter Life Cycle
~150 min
Non-synchronized average level
Transcriptome Changes
During the Cell Cycle
Expression of 16% of the Genome is Cell-Cycle Regulated
Turning it on, turning it over
Pulse/Chase
Cell Cycle
Regulation Is
Mediated by
CtrA
CtrA controls 38 direct
and 144 indirect targets
(~7% of the genome)
Resynthesis
Proteolysis
SW
ST
Frees the ORI
Represses
the ORIs
Cell Cycle
Expression
of CtrA
Asymmetric Localization of Other Key
Determinant Molecules
Proteolysis In SW
K
i
n
a
s
e
s
Localize to ST
Localize to SW
Localize to poles
and disperses
Movie
Localization
of DivJtoDuring
theduring
Cell division
Cycle
Localization
of DivJ::GFP
the ST pole
QuickTime™ and a
Planar RGB decompressor
are needed to see this picture.
MreB Organizes Polarity
Another
master
Regulator,
GcrA,
Partitions
Oppositely
from CtrA
GcrA is a Positive
Regulator of DNA
Replication in ST
The CtrA/GcrA Master Cycle
CtrA represses
GcrA expression
Proteolysis of CtrA releases
GcrA expression
GcrA expression turns
CtrA expression back on
CtrA represses
expression of itself
and GcrA
SW
molecular
identity
ST
molecular
identity
Taking
Different
Paths
Literally Sorting
out molecular
identity
A Few Questions for Thought
•Describe the Caulobacter life cycle, noting key cellular
landmarks of each stage of development.
•Extend your discussion of the prokaryotic cytoskeleton from
E. coli to include Caulobacter’s crescentin.
•Propose a model based on the Min operon system for how
Caulobacter reproducibly divides in an unequal fashion.
•Discuss the critical role of CtrA in the developmental of
Caulobacter, including a sense of when, where and why this
protein is active as well as the rich diversity of targets that it
regulates (and the consequences of those interactions).
•Describe how expression of CtrA and GcrA alternate to drive
the developmental cycle of Caulobacter.
•Explain how differential inheritance of transcription factors
and kinases can constrain two daughter cells to different
developmental fates.