Substituents at N6 and C-5′ Control Selective Uptake and Toxicity of the Adenine-Nucleotide Bacteriocin, Agrocin 84, in Agrobacteria

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Abstract
The inhibition of a sensitive strain of Agrobacterium radiobacter by the nucleotide bacteriocin agrocin 84 (an agent used in the control of crown gall tumor in dicotyledonous plants) was studied. A structure-function study of the agrocin 84 molecule was undertaken. Two agrocin 84 nucleotide fragments lacking either the N6 or 5''-phosphoramidate substituents were used in uptake studies of [32P2]agrocin 84. The plasmid-controlled, strain-specific uptake of agrocin 84 is apparently determined by the N6-D-glucofuranosyloxyphosphoramidate substituent. This is further supported by the markedly reduced uptake of the 32P-labeled fragment lacking the N6 substituent. Equilibrium dialysis studies also indicate that the N6 substituent is recognized by a binding protein involved in the uptake of agrocin 84 into sensitive strains. The nucleotide fragment bearing the N6 substituent is a competitive inhibitor for the uptake of agrocin 84 in vivo with a Ki = 1.0 .times. 10-7 M and is itself selectively transported into a sensitive strain at a rate comparable with agrocin 84, but unlike agrocin 84 is non-toxic. The fragment bearing the 5''-phosphoramidate is taken up by both sensitive and insensitive strains at a barely measurable rate and is toxic to both.