Sequence analysis of a faba bean necrotic yellows virus DNA component containing a putative replicase gene.

Faba bean necrotic yellows virus (FBNYV) has a circular ssDNA genome possibly consisting of several components of about 1 kb each. The complete nucleotide sequence of one component of FBNYV (FBNYV DNA 1) containing a putative replicase gene is presented. This component consists of 1002 nucleotides and, in the virion orientation, contains one large open reading frame (ORF1) potentially encoding a 32.3 kDa replicase with the NTP-binding motif GGEGKS. No obvious functions could be assigned to two smaller ORFs (7.4 and 9.3 kDa) occurring in the complementary orientation. Amino acid sequence comparisons of the putative replicase of FBNYV with that of other similar ssDNA viruses yielded higher homologies to subterranean clover stunt virus than to banana bunchy top and coconut foliar decay viruses. A potential stem-loop structure and a TATA box were identified within the noncoding region. Two oligonucleotides derived from FBNYV DNA 1 were used for direct sequencing of the virion ssDNA to determine its virion polarity and for amplifying part of this component by immunocapture PCR in extracts from from FBNYV-infected plants.