Nucleotide Sequence of the 3'-Terminal Region of Potato Virus T RNA.

Abstract

The partial sequence of the capillovirus potato virus T (PVT) RNA containing the 3′-terminal 2392 nucleotides, excluding the poly (A) tail, was determined from cloned cDNA. The sequence contains three open reading frames (ORFs) which encode putative proteins (in the 5′→3′ direction) of Mr>29, 000 (>29K; ORF 1), Mr 40, 451 (40K; ORF 2) and Mr 23, 596 (24K; ORF 3), followed by an untranslated region of 188 nucleotides upstream of the 3′ poly (A) tail. The 5′-proximal ORF 1 encodes a product with significant homologies to the C-terminal portions of the putative polymerase proteins of “alpha-like” supergroup of plant RNA viruses, including apple chlorotic leaf spot virus (ACLSV; closterovirus subgroup A), carlavirus, potexvirus and tymovirus. The PVT 24K protein shared several blocks of conserved amino acids with the coat proteins of filamentous viruses, i.e. ACLSV, beet yellows virus (BYV; closterovirus subgroup B), citrus tristeza virus (CTV; closterovirus subgroup C), potexvirus and carlavirus. The PVT 40K protein had homologies with putative movement proteins encoded by several plant viruses (e.g. ACLSV 50K protein). PVT and ACLSV showed a similar arrangement of three ORFs in the 3′-terminal region of their genomes. However, this arrangement differs significantly from that of BYV. The sequence represented here is the first report on the group capillovirus which was established recently. These results support a close relationship of PVT with ACLSV which is currently classified in the closterovirus subgroup A.