Mutations within noncoding terminal sequences of model RNAs of Sendai virus: influence on reporter gene expression.

A reverse-genetics system employing the chloramphenicol acetyltransferase (CAT) reporter gene has been established previously for Sendai virus. We utilized PCR-directed mutagenesis to introduce nucleotide additions, deletions, and/or substitutions within terminal Sendai virus RNA sequences. The influence of these mutations on replication-transcription of these model Sendai-CAT RNAs was analyzed by assaying CAT activity. Results from these experiments indicate that (i) Sendai-CAT RNAs expressing wild-type levels of CAT activity conform to the Sendai virus rule of six, (ii) apparent exceptions to the rule of six exist in that the 5' terminus of the Sendai-CAT RNA is more tolerant than the 3' terminus of nucleotide additions or deletions, and (iii) the 3' leader region of Sendai-CAT RNA appears to be sensitive not only to mutagenesis (single-nucleotide addition or deletion) but also to changes in its total nucleotide length.