INFLUENCE OF THE POLY(A) TAIL AND PUTATIVE POLYADENYLATION SIGNAL ON THE INFECTIVITY OF WHITE CLOVER MOSAIC POTEXVIRUS

A series of mutations has been constructed in a cDNA clone of white clover mosaic virus (WCIMV) which decreases the poly(A) tail length of run-off transcripts from 74 to 27, 10 or zero 3′-terminal (A) residues. Although transcripts with short poly(A) tails were less infectious than wild-type RNA, complete removal of the (A) tail did not abolish infectivity. Addition of nonviral nucleotides to the 3′ terminus of transcripts with no 3′-terminal (A) residues eliminated infectivity. Heterogenous-length poly(A) tails, indistinguishable from the wild type, were synthesized de novo in plants inoculated with transcripts with no 3′-terminal (A) residues, demonstrating the presence of a poly(A) polymerase activity in WCIMV-infected tissue. Mutation of a putative polyadenylation motif found in the 3′ noncoding region of WCIMV decreased the efficiency of polyadenylation of the progeny of transcripts with 10 3′-terminal (A) residues. The same mutation in transcripts with no 3′-terminal (A) residues abolished infectivity. © 1991.