MUTATIONS OF A SHUTTLE VECTOR PLASMID, PZ189, IN ESCHERICHIA-COLI INDUCED BY BORON NEUTRON CAPTURED BEAM (BNCB) CONTAINING ALPHA-PARTICLES

A shuttle vector, pZ189, carrying a bacterial suppressor tRNA marker gene (supF) was dissolved in Tris-EDTA buffer containing 0.3 M B-10-enriched boric acid and then irradiated with boron neutron captured beam (BNCB) produced by the nuclear reaction B-10 (n,alpha) Li-7 with thermal neutrons. A DNA repair-deficient mutant, KS46 (uvrA(-)), of Escherichia coli was transformed with the plasmid DNA, and the transformants carrying mutations on the supF gene were selected as nalidixic acid-resistant colonies. The mutation frequency (2.4 x 10(-4)) of pZ189 at the D-10 dose was about 70 times greater than the spontaneous rate (3.5 x 10(-6)). The plasmid mutations were analyzed using DNA sequencers; 88% of them were base substitutions. A few minus-one frameshifts (7%) and deletions (5%) were detected. Among these base substitutions, transversions of G:C to T:A (42%) and G:C to C:G (29%) predominated. Twenty-seven percent of the base substitutions were G:C to A:T transitions; no A:T to G:C transitions were detected.