Induction of mutations in bacteriophage T7 by gamma-rays: independence of host-repair mechanisms.

Amber mutants of bacteriophage T7 are reverted by gamma-rays to pseudo wild-type particles, i.e. particles able to propagate in a suppressorless host. The yield of revertants is much higher when the phage is irradiated in the presence of oxygen than when irradiated anoxically. Under particular gas conditions the efficiency of mutation induction differs by less than a factor of ten among six different amber codons in cistrons 1, 5, 6, 12, 17 and 19. The induction of mutations is not dependent on error-prone repair involving the recA or lexA genes of the host cell. It is estimated that of the damages that may be inflicted by gamma-rays upon an amber codon, fewer than 1 out of 85 results in reversion of the codon to pseudo wild-type.