Comparative evolution of the recA gene of surface and deep subsurface microorganisms (an evolutionary clock of intermediate rate). Final report Page: 4 of 8
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- JAN-15-998 09:38 oSj GRANTS 8. CONTRACTS 405 744 7487 P.03
The sequence changes found in each of the P. aeruginosa mutants led
to a single amino acid change. In strain RM8 (reA908), the change
was Ser-69 to Phe and in strain RM265 (recA102) the change was
Gly-27 to Asp. These changes were computer modeled using the
crystal structure of B. coli RecA as a template. In both cases the
changes were found to be incompatible with the wild-type structure.
The amino acid change in RM8 is within a site believed to be involved
in nucleotide binding and hydrolysis. The putative protease
constitutive nature of this mutant would be explained if this mutant
protein had not lost the ability to bind ATP but had lost the ability to
hydrolyze it. The change in RM265 occurred near the site believed to
serve as contacts between RecA polymers causing bundling and
inhibition of RecA activity. The change at this site could serve to
stabilize the polymer interactions, thus inhibiting their functions. This
would explain the apparently null phenotype of recA102. These data
are consistent with the assumption of structure-function conservation
Effects of UV and UVB Irradiation on the Expression and Function
of the recA Gene.
Solar radiation contains UVA and UVB wavelengths. UVC is
currently filtered from sun light by the ozone layer before it reaches
the earth's surface. Thus UVA and UVB radiation have greater
potential for altering survival in natural environments than does UVC.
Unfortunately,,little is known about the role of the RecA protein in
protection from and repair of damage caused by UVA and UVB. Most
studies have been done using UVC wavelengths because these are
known to be absorbed directly by DNA and have been important for
sterilization of medical devises and spaces. To evaluate the importance
of the recA gene in environmental survival of microbes, we wished to
determine the role of this gene's protein product in UVA-UVB
survival. To do this, we used as our model organism P. aeruginosa
and followed the physiological and molecular consequences of
inactivation ofithe recA gene on survival following exposure to solar
UV wavelength s. P. aeruginosa was chosen as a model because it is
an autochthougus soil and aquatic organism whose recA gene we have
studied in great detail-
P. aeruginosa =ecA mutants (both RM8 or RM265) were found to be
more sensitive to both UVA and UVB radiation than were their RecA+
isogeneic parents. Introduction of a low-copy-number plasmid
containing the loned wild-type P. aemginosa recA allele restored
UVA aid U resistance to these mutants. These data demonstrate
the involvement of the RecA protein in some, as yet undefined, way in
protection from UV wavelengths found in sun light. We also found
that the concernxation of RecA protein increased two-fold, 120
minutes after e posure to either UVA or UVB radiation suggesting
these wtjvelen th5 capable of inducing expression of the recA gene. A
functional RecA protein was found to be required for activation of
bacteriophage rophages from lysogenic cells following exposure to
UVB ranildour Prophage were not induced by exposure of their hosts
to UVA radianipn. Induction of damage-inducible (din) genes in
response to UVA or UVB radiation was also shown to be RecA
de - These data indicate that the recA gene plays a role in the
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Miller, R.V. Comparative evolution of the recA gene of surface and deep subsurface microorganisms (an evolutionary clock of intermediate rate). Final report, report, April 1, 1998; United States. (digital.library.unt.edu/ark:/67531/metadc689865/m1/4/: accessed September 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.