HEIDI B. KAPLAN
Department of Microbiology and Molecular Genetics
University of Texas Medical School
6431 Fannin, 1.765 JFB
Houston, Texas 77030

Office phone: 713-500-5448
Lab phone: 713-500-5449
Fax: 713-500-5499
E-mail: hkaplan@utmmg.med.uth.tmc.edu

PUBLICATIONS:
Yang, C. and H.B. Kaplan. 1997. Myxococcus xanthus sasS encodes a sensor
histidine kinase required for early developmental gene expression. J.
Bacteriol. 179:7759-5567.

Bowden, M.G. and H.B. Kaplan. The Myxococcus xanthus LPS O-antigen is
required for social motility and multicellular development. Mol.
Microbiol. Submitted.

Plamann, L. and H.B. Kaplan. Cell-density sensing during early development
in Myxococcus xanthus. In: Cell-Cell Signalling in Bacteria. G. Dunny and
S. Winans, Eds. ASM Press. Wahington, D.C. In press.

CURRENT RESEARCH INTERESTS:
Our research focuses on the Myxococcus signal transduction pathways
that control a class of early developmentally expressed genes that require
independent input from both starvation and a cell-density signal, termed A
signal. The best characterized member of this class is the 4521 gene. Our
major effort has been to identify the trans-acting factors that control
4521 expression. Previous work from our lab and the Kaiser lab defined the
4521 promoter as a member of the sigma-54 family. We have genetically
identified within the sasB locus SasS, a histidine protein kinase sensor,
and SasR, a response regulator, that control 4521 gene expression. We have
recently determined by in vitro phosphorylation assays that a phosphate on
SasS can transfer to SasR, suggesting that they are a cognate pair. We
plan in the future to determine the signal to which they respond and what
other elements modulate their activity.
The expression of 4521 may also be regulated by cell-surface
properties. Mutants deficient in LPS O-antigen biosynthesis show increased
4521 expression. Analysis of a number of different LPS O-antigen mutants
reveal that they are deficient in fruiting body formation, sporulation and
social motility. A detailed study of these mutants suggests that the LPS
O-antigen, similar to M. xanthus pili and fibrils, is a cell-surface
component required for social motility.

LAB NEWS:
Our lab group now includes: myself,
VISITING FACULTY:
Jane Gibson, Emeritus Professor of Biochemistry, Cornell
University, was with us for a second six months this winter and hopes to
return next year.
Poonam Gulati who is now on the faculty of the University of
Houston/Downtown will be in the lab this summer.
POSTDOC:
Dongchuan Guo
GRADUATE STUDENTS:
Gabriela Bowden, Chun Yang, Jose Rivera.
PART-TIME TECHNICIAN:
Simon Jakubowski will join our graduate program in Microbiology and
Molecular Genetics
SUMMER STUDENTS:
Gowri Pachigolla (Rice University)

CONGRATULATION to DICK XU who received his Ph.D. in March!

WELCOME to BRANDON GREENBERG, formerly an undergraduate in the Singer lab,
who will be joining us as a new graduate student this fall.


ABSTRACTS:

1) MYXOCOCCUS XANTHUS sasS ENCODES A SENSOR HISTIDINE KINASE REQUIRED FOR
EARLY DEVELOPMENTAL GENE EXPRESSION.
Chun Yang and Heidi B. Kaplan. 1997. J. Bacteriol. 179:7759-5567.

ABSTRACT
Initiation of Myxococcus xanthus multicellular development requires
integration of information concerning the cell's nutrient status and cell
density. A gain-of-function mutation, sasB7, that bypasses both the
starvation and high cell density requirements for developmental expression
of the 4521 reporter gene, maps to the sasS gene. The wild-type sasS gene
was cloned and sequenced. This gene is predicted to encode a sensor
histidine protein kinase that appears to be a key element in the
transduction of starvation and cell density inputs. The sasS null mutants
express 4521 at a basal level, form defective fruiting bodies and exhibit
reduced sporulation efficiencies. These data indicate that the wild-type
sasS gene product functions as a positive regulator of 4521 expression and
participates in M. xanthus development. The N-terminus of SasS is
predicted to contain two transmembrane domains that would locate the
protein to the cytoplasmic membrane. The sasB7 mutation, an E139K missense
mutation, maps to the predicted N-terminal periplasmic region. The
C-terminus of SasS contains all of the conserved residues typical of the
sensor histidine protein kinases. SasS is predicted to be the sensor
protein in a two-component system that integrates information required for
M. xanthus developmental gene expression.


2) THE MYXOCOCCUS XANTHUS LPS O-ANTIGEN IS REQUIRED FOR SOCIAL MOTILITY
AND MULTICELLULAR DEVELOPMENT.
M. Gabriela Bowden and Heidi B. Kaplan. Submitted to Mol. Microbiol.

SUMMARY
The gliding bacterium, Myxococcus xanthus aggregates to form spore-filled
fruiting bodies when nutrients are limiting. Defective fruiting body
formation and sporulation result from mutations in the sasA locus which
encodes the wzm wzt wbgA (formerly rfbABC) lipopolysaccharide (LPS)
O-antigen biosynthesis genes. These same sasA locus mutations result in
small glossy colonies with defective social motility. We report here that
the developmental and motility phenotypes of four mutants each containing
different Tn5 insertions in LPS O-antigen biosynthesis genes are similar to
those of the original sasA locus mutants. All of the LPS O-antigen mutants
tested exhibited defective developmental aggregation and sporulated at only
0.02 - 15% of the wild-type level. In addition, all of the LPS O-antigen
mutants were determined by genetic analyses to be wild-type for adventurous
motility and defective in social motility, indicating that the LPS
O-antigen is necessary for normal development and social motility. The two
previously identified cell surface components required for social motility,
Type IV pili and the protein-associate polysaccharide material termed
fibrils, were detected on the surfaces of all of the LPS O-antigen mutants.
This indicates that LPS O-antigen is a third cell-surface component
required for social motility.

_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/__/
Heidi B. Kaplan, Ph.D.
Assistant Professor
Department of Microbiology and Molecular Genetics
6431 Fannin, 1.765 JFB
University of Texas Medical School
Houston, TX 77030

Ph. 713-500-5448
Fx. 713-500-5499