Sequence analysis of the trailer region of sonchus yellow net virus genomic RNA

The sequence of the 5' terminus (or the "trailer" region) of the minus-sense RNA genome of sonchus yellow net virus (SYNV) was determined by dideoxynucleotide termination sequencing of purified viral RNA and cloned cDNAs. The 5'-terminal nucleotide was identified by nuclease P1 digestion of 32P-end-labeled genomic RNA followed by polyethyleneimine cellulose chromatography. The trailer sequence occupies positions 13,561 to 13,720 relative to the 3' end of the genomic RNA and is composed of 160 nucleotides (nt) adjacent to a dinucleotide forming a portion of the "gene junction" sequence at the terminus of the L protein gene. The trailer sequence is longer than the 144-nt plus-strand leader RNA transcribed from the 3' end of the genomic RNA and is the longest trailer sequence yet reported among the nonsegmented negative-strand viruses. As is characteristic of other rhabdovirus genomes, the 3' and 5' termini of the SYNV genome are complementary and are capable of forming a panhandle structure involving 16 of the 18 terminal nucleotides. However, there is no obvious direct nucleotide sequence relatedness between the SYNV trailer sequence and those of animal rhabdoviruses and paramyxoviruses. The existence of a minus-strand leader RNA of the same polarity as the trailer sequence could not be detected in nucleic acid extracted from infected plants under hybridization conditions suitable for detection of the plus-strand leader RNA. In this regard, SYNV differs from vesicular stomatitis virus and is similar to other rhabdoviruses which also fail to accumulate detectable minus-strand leader RNAs.