INFECTIOUS IN-VITRO TRANSCRIPTS FROM CLONED CDNA OF THE POTATO A-POTYVIRUS

A full-length cDNA copy of potato virus A RNA was constructed downstre am from the bacteriophage T7 RNA polymerase promoter. A single extra g uanosine not present in PVA RNA was added to the 5'-end of the cDNA. T he capped in vitro transcripts from cloned cDNA were infectious in the mesophyll protoplasts and intact plants of Nicotiana tabacum. PVA coa t protein accumulated in transcript-inoculate tobacco protoplasts and infected systemically intact plants producing high PVA titres accordin g to the ELISA and immunoblot assay. The infected tobacco plants produ ced similar mild mosaic symptoms in the systemically infected leaves, irrespective of whether the RNA transcripts or parental virus were use d as inoculum; the virus particles were also morphologically similar a ccording to immunosorbent electron microscopy.