A temperature sensitive nonsense mutation affecting the synthesis of a major protein of Escherichia coli K12.

A temperature sensitive nonsense (TSN) mutant of E. coli K12 has been isolated in which a major bacterial protein is not synthesized at 42 degrees C. This protein is found in the parental strain at 42 degrees C and in cells rendered temperature resistant due to the insertion of a number of different nonsense suppressors or the normal allele of the mutant locus.