Mistranslation in E. coli

Abstract

Flagellin, the protomeric subunit of bacterial flagella, contains no cysteine. We have detected the incorporation of trace quantities of 35S-cysteine into flagellin, highly purified and then resolved by SDS polyacrylamide gel electrophoresis, to measure mistranslation in vivo. Under normal conditions, this value is about 6 × 10 −4 pmoles cysteine per pmole flagellin. This value is greatly increased during growth in low concentrations of streptomycin and neomycin, antibiotics which are known to stimulate misreading in vitro. Of the specific types of misreading which streptomycin stimulates in vitro, only misreading of the CGU and CGC arginine codons could give rise to illegitimate incorporation of cysteine. In agreement, partial arginine starvation increases the incorporation of 35S-cysteine into flagellin in a relA mutant, with or without streptomycin, but has no such effect in its isogenic relA + partner. Assuming from these results that 35S-cysteine incorporation into flagellin reflects misreading of CGU/C coda, we deduce a misreading probability per codon in the range of 10 −4.