Rm. Vijesurier et al., Role and mechanism of action of C center dot PvuII, a regulatory protein conserved among restriction-modification systems, J BACT, 182(2), 2000, pp. 477-487
The PvuII restriction-modification system is a type II system, which means
that its restriction endonuclease and modification methyltransferase are in
dependently active proteins. The PvuII system is carried on a plasmid, and
its movement into a new host cell is expected to be followed initially by e
xpression of the methyltransferase gene alone so that the new; host's DNA i
s protected before endonuclease activity appears. Previous studies have ide
ntified a regulatory gene (pvuIIC) between the divergently oriented genes f
or the restriction endonuclease (pvuIIR) and modification methyltransferase
(pvuIIM), with pvuIIC in the same orientation as and partially overlapping
pvuIIR, The product of pvuIIC, C . PvuII, was found to act in trans and to
be required for expression of pvuIIR. In this study we demonstrate that pr
emature expression of pvuIIC prevents establishment of the PvuII genes, con
sistent with the model that requiring C . PvuII for pvuIIR expression provi
des a timing delay essential for protection of the new host's DNA, We find
that the opposing pvuIIC and pvuIIM transcripts overlap by over 60 nucleoti
des at their 5' ends, raising the possibility that their hybridization migh
t play a regulatory role. We furthermore characterize the action of C . Pvu
II, demonstrating that it is a sequence-specific DNA-binding protein that b
inds to the pvuIIC promoter and stimulates transcription of both pvuIIC and
pvuIIR into a polycistronic mRNA. The apparent location of C . PvuII bindi
ng, overlapping the - 10 promoter hexamer and the pvuIICR transcriptional s
tarting points, is highly unusual for transcriptional activators.