THE PUTATIVE REPLICASE OF THE COCKSFOOT MOTTLE SOBEMOVIRUS IS TRANSLATED AS A PART OF THE POLYPROTEIN BY -1 RIBOSOMAL FRAMESHIFT

The polyprotein of cocksfoot mottle sobemovirus (CfMV) is encoded by t wo overlapping open reading frames (ORF). The ORF 2a codes for the put ative VPg and serine protease and the ORF 2b codes for the putative re plicase. The consensus signals for a -1 ribosomal frameshifting event are found at the very beginning of the overlapping region of these ORF s. The shifty heptanucleotide in CfMV is UUUAAAC, and the secondary st ructure after the shifty sequence is predicted to be a stem-loop. in v itro translation of the CfMV RNA in wheat germ extract produced protei ns of several sizes, including one of 100 kDa. According to the nucleo tide sequence data, no single ORF is capable of directing the synthesi s of a 100-kDa protein. A chimeric beta-glucuronidase-CfMV cDNA contai ning the entire ORF 2a and 2b overlap region including frameshift sign als was constructed. A trans-frame protein of 108 kDa was produced fro m this construct with an efficiency of 26-29% by in vitro translation in wheat germ extract. CfMV is the first sobemovirus in which the puta tive replicase is reported to be produced as a part of a polyprotein b y a -1 frameshift event. The replicases of the sobemoviruses are relat ed to the luteovirus subgroup II replicases, which are known to be pro duced by -1 ribosomal frameshift. The reported amino acid sequences of the putative replicases of sobemo- and subgroup II luteoviruses were compared to that of the putative replicase of CfMV. This comparison re vealed more extensive homology between these groups than previously re ported. (C) 1995 Academic Press, Inc.