CHARACTERIZATION OF THE ACC OPERON FROM THE NOPALINE-TYPE TI PLASMID PTIC58, WHICH ENCODES UTILIZATION OF AGROCINOPINE-A AND AGROCINOPINE-BAND SUSCEPTIBILITY TO AGROCIN-84

The acc locus from the Ti plasmid pTiC58 confers utilization of and ch emotaxis toward agrocinopines A and B (A+B), as well as susceptibility to a highly specific antiagrobacterial antibiotic, agrocin 84. DNA se quence analyses revealed that acc is composed of eight open reading fr ames, accR and accA through accG. Previous work showed that accR encod es the repressor which regulates this locus, and accA codes for the pe riplasmic binding protein of the agrocinopine transport system (S. Bec k Von Bodman, G. T. Hayman, and S. K. Farrand, Proc. Natl. Acad. Sci. USA 89:643-647, 1992; G. T. Hayman, S. Beck Von Bodman, H. Kim, P. Jia ng, and S. K. Farrand, J. Bacteriol. 175:5575-5584, 1993). The predict ed proteins from accA through accE, as a group, have homology to prote ins that belong to the ABC-type transport system superfamily. The pred icted product of accF is related to UgpQ of Escherichia coli, which is a glycerophosphoryl diester phosphodiesterase, and also to agrocinopi ne synthase coded for by acs located on the T-DNA. The translated prod uct of accG is related to myoinositol 1 (or 4) monophosphatases from v arious eucaryotes. Analyses of insertion mutations showed that accA th rough accE are required for transport of both agrocin 84 and agrocinop ines Af B, while accF and accG are required for utilization of the opi nes as the sole source of carbon. Mutations in accF or accG did not ab olish transport of agrocin 84, although we observed slower removal of the antibiotic from the medium by the accF mutant compared to the wild type. However, the insertion mutation in accF abolished detectable up take of agrocinopines A+B. A mutation in accG had no effect on transpo rt of the opines. The accF mutant was not susceptible to agrocin 84 al though it took up the antibiotic. This finding suggests that agrocin 8 4 is activated by AccF after being transported into the bacterial cell .