Influence of a Functional sigB Operon on the Global Regulators sar and agr in Staphylococcus aureus

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Abstract
The vir genes of octopine, nopaline, andl,l-succinamopine Ti plasmids exhibit structural and functional similarities. However, we observed differences in the interactions between octopine and nopalinevir components. The induction of an octopinevirE A6::lacZ fusion (pSM358cd) was 2.3-fold higher in an octopine strain (A348) than in a nopaline strain (C58). Supplementation of the octopinevirG A6 in a nopaline strain with pSM358 did not completely restore virE A6 induction. However, addition of the octopine virA A6 to the above strain increased virE A6 induction to a level almost comparable to that in octopine strains. In a reciprocal analysis, the induction of a nopalinevirE C58::cat fusion (pUCD1553) was two- to threefold higher in nopaline (C58 and T37) strains than in octopine (A348 and Ach5) andl,l-succinamopine (A281) strains. Supplementation of nopaline virA C58 andvirG C58 in an octopine strain (A348) harboring pUCD1553 increased induction levels ofvirE C58::cat fusion to a level comparable to that in a nopaline strain (C58). Our results suggest that octopine and l,l-succinamopine VirG proteins induce the octopine virE A6 more efficiently than they do the nopaline virE C58. Conversely, the nopaline VirG protein induces the nopalinevirE C58 more efficiently than it does the octopine virE A6. The ability of Bo542virG to bring about supervirulence in tobacco is observed for an octopine vir helper (LBA4404) but not for a nopaline vir helper (PMP90). Our analyses reveal that quantitative differences exist in the interactions between VirG and vir boxes of different Ti plasmids. Efficientvir gene induction in octopine and nopaline strains requires virA, virG, andvir boxes from the respective Ti plasmids.