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Bacillus halodurans
RecA-DNA binding and RecA-mediated cleavage
enhancing at
alkaliphilic
pH in vitro
Dieudonné Ndjonka1, 2*
and Charles E. Bell1
1Department
of Molecular and Cellular Biochemistry, Ohio State
University College of Medicine, Columbus, OH 43210.
2Current
Address: University of Ngaoundéré, Faculty of Science,
Department of Biological Sciences, P. O. Box 454, Ngaoundéré,
Cameroon.
*Corresponding author. E-mail:
dede_ndjonka@yahoo.com. Tel.: 237 7705 2511.
Accepted
9 March, 2009 |
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In Escherichia coli, RecA protein catalyzes DNA
pairing and strand exchange activities essential for genetic
recombination. This is critical for normal cellular function
under conditions that lead to altered DNA metabolism and DNA
damage. The RecA proteins of E. coli and Bacillus
halodurans both can bind to DNA and catalyze the
specific proteolytic cleavage of LexA and lambda repressor
which induces SOS response. At neutral pH self-cleavage of
LexA depends exclusively on its binding to RecA filament,
while at elevated pH (~10) it autodigests in the absence of
RecA. We have shown in this work that the RecA-mediated
cleavage and the binding of RecA to DNA promoted by B.
halodurans are similar to those promoted by E. coli
RecA, excepted that in the case of B. halodurans the
rate of the cleavage reactions is increased at alkaline pH
and that NaCl favors the binding of RecA to DNA. The results
lead to two hypotheses for the pathway for RecA-mediated
cleavage, in which we first suppose that the internal pH of
the bacteria is neutral. Thus LexA cannot undergo
autodigestion, the genes involving in DNA repair and
replication are not transcribed, regulating the growth of
the cell. The second hypothesis is that the external
environment and the internal pH of the bacteria are
alkaline; here also the bacteria may have developed
strategies to maintain LexA not inactivated. These
observations suggest that the LexA autodigestion in B.
halodurans at high pH may be regulated at the
transcriptional level and that B. halodurans may be
haloalkaliphile bacterium.
Key words:
DNA binding,
haloalkaliphile, autodigestion. |
