Biological activity of T7 transcripts of a prototype clone and a sequence variant clone of a satellite RNA of cucumber mosaic virus.

Molecular cloning of the (D)CARNA 5 (previously known as n-CARNA 5) necrosis-inducing satellite RNA of cucumber mosaic virus produced a prototype clone (pDsat4) and a sequence variant clone (pDsat1). pDsat1 contained 10 nucleotide changes between positions 70 and 160 which rendered that region identical to the corresponding region of a satellite RNA which does not induce necrosis. T7 RNA polymerase transcripts of each clone replicated in both tobacco and tomato, and the progeny satellite RNAs did not retain the 57-nucleotide non-satellite sequence at the 5' ends of the T7 transcripts. RNase T1 fingerprint analysis of both T7 transcripts and progeny satellite RNAs proved that the satellite sequence portion of each transcript was faithfully replicated in tobacco, and the variations in pDsat1 relative to pDsat4 were maintained. Replication of transcripts of either pDsat4 or pDsat1 in tomato resulted in lethal necrosis, suggesting that the determinant of necrosis induction lies outside the region between nucleotides 70 and 160.