CONSTRUCTION OF A NEW SYSTEM FOR SEPARATE EXPRESSION OF MUTAGENESIS PROTEINS - THE ABILITIES TO PROMOTE UV MUTAGENESIS AND INTERCHANGEABILITY OF MUCA', MUCB, SAMA' AND SAMB PROTEINS IN SALMONELLA-TYPHIMURIUM
P. Gruz et al., CONSTRUCTION OF A NEW SYSTEM FOR SEPARATE EXPRESSION OF MUTAGENESIS PROTEINS - THE ABILITIES TO PROMOTE UV MUTAGENESIS AND INTERCHANGEABILITY OF MUCA', MUCB, SAMA' AND SAMB PROTEINS IN SALMONELLA-TYPHIMURIUM, Mutation research, 354(2), 1996, pp. 157-170
The two distinct mucAB and samAB operons originally isolated from the
plasmids of Salmonella typhimurium encode proteins engaged in induced
mutagenesis. They represent two extreme cases among these far characte
rized members of the enterobacterial umuDC family in respect to both t
he strength and the specificity of their effect. It is suggested that
the MucA and SamA proteins are post-translationally processed to MucA'
and SamA', respectively, which lack the N-terminal 25 amino acids and
are the active species in mutagenesis. For the purpose of characteriz
ing the individual activities of these proteins, we developed a new sy
stem for their SOS-independent separate and controllable expression in
enterobacteria. Besides the matured forms of MucA', SamA' as well as
MucB and SamB proteins we also expressed hybrid HisTag-MucA' and HisTa
g-SamA' proteins in which a synthetic 24 amino acid HisTag region repl
aces the natural 25 amino acid N-terminal leader present in the MucA a
nd SamA precursors. In this study, we analyzed the effect of the mutag
enesis proteins on the UV mutability of S. typhimurium YG5144. None of
the proteins, if expressed alone, promoted UV mutagenesis. Different
combinations of the proteins promoted mutagenesis to different extents
in the order MucA' + MucB > SamA' + SamB greater than or equal to His
Tag-MucA' + MucB greater than or equal to SamA' + MucB > MucA' + SamB
> HisTag-SamA' + SamB. The mutagenesis enhancing potential of the comb
inations with MucB protein decreased as the expression of the proteins
increased while the mutagenesis enhancing potential of the combinatio
ns with SamB protein increased together with the increase in the expre
ssion. The artificially expressed MucA' + MucB proteins were as active
as their MucAB counterparts expressed from the plasmid pKM101 in prom
oting UV mutagenesis, but they were remarkably more efficient than the
ir pKM101-born counterparts in promoting spontaneous mutagenesis. We c
onclude that the MucA'B and SamA'B proteins are partly interchangeable
and the functionality of the resulting A' + B complex is largely depe
ndent on the appropriate B-protein.