|
|
 |
BIOGRAPHY:
Dr. Mizrahi earned her Ph.D. in chemistry from the University of Cape Town in 1983. From 1983 until 1986 she did postdoctoral work at the Pennsylvania State University. She subsequently held positions with the South African Council for Scientific and Industrial Research, Smith Kline & French Research & Development, the University of the Witwatersrand, and the South African Institute for Medical Research. She was recently named Director of a newly created Molecular Mycobacteriology Research Unit jointly funded by the South African Medical Research Council, the South African Institute for Medical Research and the University of the Witwatersrand. Her HHMI-funded project is entitled "The Individual and Collective Roles of Y Family DNA Polymerases in
Genetic Adaptation and Long-Term Survival of Mycobacteria."
RESEARCH ABSTRACT SUMMARY:
The Individual and Collective Roles of Y Family DNA Polymerases in Genetic Adaptation and Long-Term Survival of Mycobacteria
The alarming increase in multidrug resistance in Mycobacterium
tuberculosis is attributable to the evolution and global spread of
strains that carry multiple chromosomal mutations. As such, there is
considerable interest in defining the mutational mechanisms that
operate in mycobacteria. We recently found that induced (SOS) base
substitution mutagenesis in mycobacteria is mediated by DnaE2, a novel,
damage-inducible C-family DNA polymerase. DnaE2 is the first example of
a growing number of DnaE-type polymerases from gram-positive bacteria
that catalyze error-prone repair synthesis. The central role of DnaE2
in damage tolerance in mycobacteria is particularly surprising in light
of the presence in mycobacteria of multiple umuC-like genes
encoding members of the Y-family of low-fidelity DNA polymerases, which
are responsible for SOS mutagenesis in other bacteria. We are adopting
an integrated genetic, biochemical, and physiological approach to
investigate the individual and collective roles of the two Y-family
polymerases of M. tuberculosis and the three of M.
smegmatis in genetic adaptation and long-term survival in these
organisms. To this end, a large panel of mutant strains with altered
expression of the Y-family polymerase-encoding genes has been
constructed, which includes a mutant of M. smegmatis that lacks
all three umuC-like genes. To determine the effects of altered
levels of Y-family polymerases on mutagenesis in M.
smegmatis and M. tuberculosis, we are measuring mutation
rates by fluctuation analysis and elucidating the mutational spectra in
various genetic backgrounds using endogenous or specifically engineered
chromosomal mutational targets for monitoring base substitutions
(rpoB, hisD), frameshift mutations (hisD), and
mutations at GC-rich (PE-PGRS) repeat loci. This mutational approach is
being supplemented by biochemical studies aimed at characterizing the
DNA polymerase activity of a recombinant form of the M.
tuberculosis DinX protein and by expression studies aimed at
elucidating the transcriptional regulation of these genes.
Photo: Kent Kallberg, Kallberg Studios
|
