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Our laboratory has been studying the molecular mechanisms of
mutagenesis and DNA repair using
Escherichia
coli as a
model organism. Most recently we have been trying to
characterize spontaneous mutagenesis as it occurs under
starvation conditions. Using the Trp+ reversion
system we have shown that mutagenesis clearly occurs under
starvation conditions and this requires the
recA
and umuC genes and oxygen16. Moreover this
starvation-associated mutagenesis occurs at a much higher
frequency in the presence of the
mucAB
genes (homologues of
umuDC) located in the pKM101 plasmid (R.G. Fowler and B.B Gadea,
unpublished observations). Perhaps more importantly, it was
also shown the E.
coli cells
survive starvation better with the
muc
genes of pKM101.
Proposed Undergraduate Role in the Investigation
The
undergraduate students participating in RUMBA will serve a vital
role in this investigation by characterizing starvation
mutagenesis in pKM101. RUMBA students will have the
opportunity to develop and test their own ideas within the
framework of this research. Examples of possible
projects students can become interested in investigating are:
(1) characterization of starvation mutagenesis and the enhanced
survival with pKM101 more fully in the proposed experiments, and
(2) studying the effect oxygen may have on the ability of pKM101
to confer an increase in cell survival.
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Dr. Fowler in his office.
We wish also to characterize the enhanced survival that
pKM101 provides to starving strains and determine how it may be
related to the increase in starvation mutagenesis. A number of
recent studies have found the occurrence of increased mutation
rates to be associated with stressful environments (e.g., Taddei
et al.,
1995) and the explanation for this association is that an
increase in number of mutations may lead to some adaptive
mutations that could allow survival in a stressful environment.
An alternative explanation is that under stress there is an
increase is some form of DNA repair which is error-prone in
nature. With this explanation, the increase in mutations is
simply a by-product of increased repair. We will try to
distinguish between these two explanations for increased
survival by pKM101 by seeing if increases in survival also occur
when cells are plated in agar plates with no carbon source at
all. In this case it is difficult to assume that simple
mutations would increase survival and if increased survival does
occur it would suggest that increased DNA repair is a more
reasonable explanation.
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