Abstract :
Northern blot analysis of double-stranded (ds) RNA from bean-leaf
tissue infected with tobacco necrosis virus strain D (TNV-D) detected
the 4 kb genomic RNA and two subgenomic RNAs of about 1.5 kb
and 1.2 kh; RNA extracted from virus particles only contained the
genomic species. Blotting and probing with a range of probes indicated
the approximate locations of the 5ʹ ends of subgenomic RNA so that
primers to fine-map the ends could be designed. When both singlestranded
and ds RNA, extracted from TNV-D infected and healthy
bean leaves were used as templates for primer extension using primers
complementary to sequences at, or upstream of, the initiation codons
of, respectively, the coat protein and the p7a genes, major infectionspecific
products were detected. Both subgenomic RNAs start at G
residues. The larger subgenomic RNA is 1547 nucleotides in length
with a leader sequences of 36 nucleotides upstream ofthe p7a gene, and
the smaller subgenomic RNA has a 90 nucleotide leader upstream of
the coat protein AUG and is 1202 nucleotides long. An analysis ofthe
5ʹ terminal locations of both subgenomic RNAs and the previously
mapped analogous subgenomic RNAs associated with infection with
the related TNV-A isolate, revealed a marked degree of homology
downstream of the initiation sites for each RNA, This homology was
maintained at the 5ʹ termini of both virion RNAs and could be extended
to another isolate of TNV for which partial sequence data, but not
subgenomic mapping RNA data are available.
