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Molecular Plant Pathology

Potato Leaf Roll Virus 3? Genome Organization: Sequence of the Coat Protein Gene and Identification of a Viral Subgenomic RNA. O. P. Smith, Research plant pathologist, U. S. Department of Agriculture, Agricultural Research Service, Foreign Disease-Weed Science Research, Fort Detrick, Bldg. 1301, Frederick, MD 21701; K. F. Harris, Professor, Department of Entomology, Texas A&M University, College Station 77843. Phytopathology 80:609-614. Accepted for publication 28 November 1989. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1990. DOI: 10.1094/Phyto-80-609.

The nucleotide sequence of the 3? portion of the potato leaf roll virus (PLRV, isolate 4) genome representing 2,361 bases has been determined from cloned cDNA. The identity of the open reading frame (ORF) encoding the coat protein was confirmed by expression of an Escherichia coli ?-galactosidase fusion protein and detection by a dot blot immunoassay. The coat protein gene contains 624 nucleotides and encodes a protein of 208 amino acids with a calculated molecular weight of 23.2 kDa. This gene is located internal to the 3?-end of the genome, contains the complete overlap of an ORF encoding a 17.4 kDa protein, and is followed in-frame by an ORF encoding a 56.4 kDa protein. Northern blot hybridization experiments have identified a 3?-positioned viral subgenomic RNA (approximately 2.5 kb) produced in PLRV-infected plants. This subgenomic RNA is not encapsidated and, by analogy to other RNA plant viruses, is likely the mRNA for expression of the 3? portion of the genome. A comparison of the PLRV-4 coat protein sequence with two other luteoviruses, beet western yellows virus (isolate FL1) and barley yellow dwarf virus (isolate PAV) has revealed amino acid sequence similarities of 64 and 45%, respectively. The coat protein stop codon (TAG) of all three luteoviruses is contained within a conserved 14-nucleotide sequence (CCAAATAGGTAGAC).