Temperature-inducible amber suppressor: construction of plasmids containing the Escherichia coli serU- (supD-) gene under control of the bacteriophage lambda pL promoter.

An Escherichia coli DNA fragment containing the structural gene serU132 for the nonsense suppressor tRNASer2am was identified and purified by being cloned into a plasmid vector. Information obtained from DNA sequence analysis was used to select a serU132 fragment for insertion downstream from the bacteriophage lambda pL promoter in two pBR322-lambda derivatives. In nonsense mutant strains bearing the resulting serU132 hybrid plasmids, the presence of the lambda cI857 repressor gene carried on the same plasmid or in a prophage genome permits thermal regulation of suppressor synthesis.