Further characterization of conditional lethal amber nonsense mutants of vesicular stomatitis virus: nucleotide sequence analysis.

Conditional lethal amber nonsense mutants of vesicular stomatitis virus, Indiana serotype, classified in complementation group I (the L gene), synthesize truncated versions of the L protein. This paper reports further characterization of mutants AmbL1, AmbL2 and AmbL3 by nucleic acid sequence analysis, which was achieved by sequencing L mRNA directly using appropriate synthetic oligonucleotides. In each case a single point mutation altered a glutamine-specifying codon to an amber stop codon. The L mRNA from wild-type and revertant viruses was sequenced for comparison. Of the revertants sequenced, each had reverted by back mutation within the same codon as the original mutation. A revertant of AmbL2 reverted by a second site mutation, also within the same codon as the original mutation. These mutants may be useful for assigning functions to different parts of the L polypeptide chain.