Deletion analysis of the 5' untranslated leader sequence of tobacco mosaic virus RNA.

To determine the sequences essential for viral multiplication in the 5' untranslated leader sequence of tobacco mosaic virus RNA, mutant TMV-L (a tomato strain) RNAs which carry several deletions in this 71-nucleotide sequence were constructed by an in vitro transcription system and their multiplication was analyzed by introducing mutant RNA into tobacco protoplasts by electroporation. Large deletions of the sequence from nucleotides 9 to 47 or 25 to 71 abolished viral multiplication; when about 10-nucleotide deletions were introduced throughout this 5' leader sequence, only deletion of the sequence from nucleotides 2 to 8 abolished detectable viral multiplication. This mutant RNA, however, directed the synthesis of the 130,000-molecular-weight protein in a rabbit reticulocyte lysate in vitro translation system, and consequently this 5'-proximal portion appears likely to be essential for replication.