TY - JOUR
T1 - Enhanced monomer-monomer interactions can suppress the recombination deficiency of the recA142 allele
AU - Zaitsev, Eugene N.
AU - Kowalczykowski, Stephen C.
PY - 1999
Y1 - 1999
N2 - The RecA142 protein, in which valine is substituted for isoleucine-225, is defective for genetic recombination in vivo and for DNA strand exchange activity in vitro under conventional growth and reaction conditions respectively. However, we show that mildly acidic conditions restore both the in vitro DNA strand exchange activity and the in vivo function of RecA142 protein, suggesting that recombination function can be restored by a slight change in protein structure elicited by protonation. Indeed, we identified an intragenic suppressor of the recombination deficiency of the recA142 allele. This suppressor mutation is a substitution of leucine for glutamine at position 124. Based on the three-dimensional structure, the Q-124L substitution is predicted to make a new monomer-monomer contact with residue phenylalanine-21 of the adjacent RecA monomer. The Q-124L mutation is not allele specific, because it also suppresses the recombination deficiency of a recA deletion (Δ9), lacking nine amino acids at the amino-terminus, presumably by reinforcing the monomer-monomer interactions that are attenuated by the Δ9 deletion. Expression of RecA(Q-124L) protein is toxic to Escherichia coli, presumably because of enhanced affinity for DNA. We speculate as to how enhanced monomer-monomer interactions and acidic pH conditions can restore the recombination activity of some defective recA alleles.
AB - The RecA142 protein, in which valine is substituted for isoleucine-225, is defective for genetic recombination in vivo and for DNA strand exchange activity in vitro under conventional growth and reaction conditions respectively. However, we show that mildly acidic conditions restore both the in vitro DNA strand exchange activity and the in vivo function of RecA142 protein, suggesting that recombination function can be restored by a slight change in protein structure elicited by protonation. Indeed, we identified an intragenic suppressor of the recombination deficiency of the recA142 allele. This suppressor mutation is a substitution of leucine for glutamine at position 124. Based on the three-dimensional structure, the Q-124L substitution is predicted to make a new monomer-monomer contact with residue phenylalanine-21 of the adjacent RecA monomer. The Q-124L mutation is not allele specific, because it also suppresses the recombination deficiency of a recA deletion (Δ9), lacking nine amino acids at the amino-terminus, presumably by reinforcing the monomer-monomer interactions that are attenuated by the Δ9 deletion. Expression of RecA(Q-124L) protein is toxic to Escherichia coli, presumably because of enhanced affinity for DNA. We speculate as to how enhanced monomer-monomer interactions and acidic pH conditions can restore the recombination activity of some defective recA alleles.
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U2 - 10.1046/j.1365-2958.1999.01552.x
DO - 10.1046/j.1365-2958.1999.01552.x
M3 - Article
C2 - 10540281
AN - SCOPUS:0032822925
VL - 34
SP - 1
EP - 9
JO - Molecular Microbiology
JF - Molecular Microbiology
SN - 0950-382X
IS - 1
ER -