EVIDENCE THAT VIRION-ASSOCIATED VP1 OF AVIBIRNAVIRUSES CONTAINS VIRAL-RNA SEQUENCES

The VP1 encoded by genomic segment B of birnaviruses is generally know n to exist as a genome-linked protein (VPg) and as a ''free'' polypept ide of 90 kDa in virus particles. The guanylylation activity associate d with infectious bursal disease virus (IBDV) was demonstrated by incu bating purified virus in presence of [alpha(32)P] GTP; optimum activit y in the 90 kDa form of VP1 was seen in low salt concentration in the presence of 4 mM magnesium ions over a wide range of incubation temper atures. The IBDV VP1 was shown to lack guanyl transferase activity. No rthwestern (RNA-protein) blot analysis of purified virus using a radio labeled cDNA probe consisting of 3' and 5' ends of genomic segment B i ndicated that both forms of virion-associated VP1 contained viral RNA sequences of which those linked to VPg corresponded to the two genome segments and those linked to the 90 kDa VP1 were probably a short olig onucleotide of the terminal viral RNA sequences.