Additional Rep-encoding DNAs associated with banana bunchy top virus

Banana bunchy top nanovirus (BBTV) has a multicomponent circular single-str anded DNA (cssDNA) genome consisting of at least six components. We have cl oned, sequenced and analysed two additional cssDNA components, designated B BTV-S1 and S2, associated with a Taiwanese BBTV isolate. The sequences of B BTV-S1 and S2 comprised 1109 and 1095 nucleotides (nt), respectively, and l ike BBTV DNA-1, potentially encoded replication initiation proteins (Reps). However, the genome organisation of BBTV-S I and S2 differed from that of BBTV DNA-1 in that (i) the stem sequence of the CR-SL was not conserved, (i i) the internal gene was absent and (iii) the probable TATA boxes were loca ted 5' of the stem-loop. Further, sequence and phylogenetic analysis of the Rep genes indicated that BBTV DNA-S 1 and S2 were distinct from BBTV DNA-1 . When different geographical isolates of BBTV were tested for the presence of BBTV-S1/S2, these components were detected in various isolates from Vie tnam, Taiwan, the Philippines, Tonga and Samoa but were not detected in iso lates from Australia, Egypt, Fiji, and India. Based on these results, BBTV- S1 and S2 do not appear to be integral components of the BBTV genome and re present additional Rep-encoding DNAs associated with BBTV.