Large deletion mutants of Escherichia coli tRNA₁^Tyr

Two suppressor-negative derivatives (9311 and 9313) of bacteriophage φ80su3⁺ have been shown to contain deletions of 110 base-pairs starting in the 3′-terminal part of the tRNA₁^Tyr gene and extending downstream. These mutations delete a 3′-proximal RNA processing site, thereby leading to the accumulation of an abnormal, unstable gene transcript. One of the suppressor-negative derivatives (9313) contains a second deletion of 178 base-pairs further downstream from the first one. The ability of 9313 to regain the parental su3⁺ phenotype with a frequency of 1% may be related to the presence of the second deletion. The deletions, which resulted originally from an ICR364-OH (an aza-quinacrine compound)-induced mutagenic event, have exactly repeated sequences of nine and six base-pairs, respectively, at their termini.