The complete nucleotide sequence of turnip yellow mosaic virus (TYMV) genomic RNA has been determined on a set of overlapping cDNA clones using a sequential sequencing strategy. The RNA is 6318 nucleotides long, excluding the cap structure. The genome organization deduced from the sequence confirms previous results of in vitro translation. A novel open reading frame (ORF) putatively encoding a Pro-rich and very basic 69K (K = kilodalton) protein is detected at the 5' end of the genome. It is initiated at the first AUG codon on the RNA and overlaps the major ORF that encodes the non structural 206K (previously referred to as 195K) protein of TYMV; its function is unknown. Several amino acid consensus sequences already described among plant and animal viruses are also found in the TYMV-encoded polypeptides. A comparison with other viruses whose RNA sequence is known leads to the conclusion that TYMV belongs to the "Sindbis-like" supergroup of viruses and could be related to Semliki forest virus.

An increasing number of examples of translational regulation at the level of termination has been recently reported in eukaryotes. This paper reviews our present knowledge on this topic and proposes an understanding of these regulations by relating the study of viral gene expression to a comprehensive view of the mechanisms and components of the translational process.

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