Nucleotide sequence of potato leafroll luteovirus RNA

A sequence of 5987 nucleotides is reported for the RNA of potato leafroll luteovirus (PLRV). The sequence contains six large open reading frames, and non-coding regions of 174 nucleotides at the 5' end, 141 nucleotides at the 3' end and 197 nucleotides between two large blocks of coding sequences. The 5' coding region encodes two polypeptides of 28,000 (28K) and 70K which overlap in different reading frames and circumstantial evidence suggests that the third open reading frame in the 5' block is translated by frameshift readthrough near the end of the 70K polypeptide to give a 118K polypeptide. The C-terminal part of the 118K protein contains the consensus sequence for RNA-dependent RNA polymerases. In vitro translation of PLRV RNA resulted in the synthesis mainly of 28K and 70K polypeptides and the largest product made was about 125K; these sizes are similar to those predicted for the translation products of the 5' block of coding sequence. The 3' block of coding sequence codes for three polypeptides: a 23K coat protein, a 17K polypeptide which is encoded in a different frame, and a 53K polypeptide which immediately follows the coat protein coding sequence, and is in the same reading frame. Circumstantial evidence suggests that the 53K polypeptide is translated by readthrough of the amber termination codon of the coat protein gene. The amino acid sequences encoded by the 3' block of coding sequence show many similarities with analogous polypeptides translated from the nucleotide sequences of RNA of barley yellow dwarf virus, PAV strain (BYDV) and, in particular, beet western yellows virus (BWYV). The 118K polypeptide has some similarities with the putative polymerase of southern bean mosaic virus and much more extensive similarities with the corresponding BWYV polypeptide but almost none with that of BYDV. In contrast, the amino acid sequence of the 28K polypeptide is not like that of proteins of the other luteoviruses or of viruses in other groups. The nucleotide sequences reported will appear in the EMBL, GenBank and DDBJ databases under the accession number X14600.