IN-VITRO TRANSCRIPTS OF TURNIP YELLOW MOSAIC-VIRUS ENCOMPASSING A LONG 3' EXTENSION OR PRODUCED FROM A FULL-LENGTH CDNA CLONE HARBORING A 2KB-LONG PCR-AMPLIFIED SEGMENT ARE INFECTIOUS

Two types of full-length cDNA clones have been constructed correspondi ng to the entire genome of turnip yellow mosaic virus (TYMV), from whi ch infectious transcripts devoid of 5' non-viral extensions can be syn thesized in vitro. The first type of transcript (tTYFL7) harbours 75 n on-viral nucleotides at its 3' end, whereas the second type (tTYFL84) possesses only 2 non-viral nucleotides at its 3' end. The 2 kilobase-l ong 3' region of tTYFL84 derives from amplification by the polymerase chain reaction of the corresponding TYMV cDNA. Both tTYFL7 and tTYFL84 are infectious in rapeseed protoplasts and plants. tTYFL7 is far less infectious than wild-type TYMV RNA and somewhat less infectious than tTYFL84. The possible effects of the 3' extraviral sequences of tTYFL7 and the heterogeneity observed in the infectivity of other transcript s prepared as was tTYFL84 are discussed.