PETUNIA VEIN-CLEARING VIRUS - A PLANT PARARETROVIRUS WITH THE CORE SEQUENCES FOR AN INTEGRASE FUNCTION

Petunia vein-clearing virus (PVCV) is a plant pararetrovirus that has some features of retrotransposons. It encapsidates dsDNA and has isome tric particles and inclusion bodies similar to those of caulimoviruses . The PVCV genome of 7205 bp has two large ORFs in the transcribed str and and a methionine tRNA primer-binding site in its 663-bp intergenic region. The N-terminal position of the large protein (126 kDa) encode d by ORF I has similarity to the movement protein of caulimoviruses. T oward the C-terminus of this same polyprotein are the two distinctive sequence elements [HHCC and DD(35)E] of the integrase function of retr oviruses and retrotransposons. ORF II of PVCV encodes a protein of 125 kDa with domains for an RNA-binding element, common to the gag gene o f retroelements, followed by consensus sequences for an acid protease, reverse transcriptase, and ribonuclease H. Hence, the gag equivalent (capsid protein) and pol gene of PVCV are part of the same polyprotein . Phylogenetic comparison or the reverse transcriptase of PVCV with th at of various other retroelements grouped PVCV between caulimoviruses and the Ty3/gypsy retrotransposons, suggesting that PVCV is a divergen t member of the caulimoviruses. (C) 1997 Academic Press.