- Volume 74, Issue 5, 1993

Tobacco mosaic virus mutant Ni 2519 has a selected temperature-sensitive defect in the spreading of local lesions, and additional reported defects in virus assembly and in host range. Here we show that the temperature-sensitive local lesion-spreading defect (which maps in the assembly origin within the gene encoding protein p30) is probably independent of mutations in the pseudoassembly origin or of host range defects resulting from other mutations in the coat protein. One new host range mutant has been isolated.

The 5′ termini of linear forms of avocado sunblotch viroid (ASBVd) isolated from infected tissue have been determined by primer extension analyses. According to the different termini identified, four main populations of linear viroid molecules were found. One of them had the same 5′ end as the one produced in the in vitro self-cleavage reaction of ASBVd dimeric transcripts mediated by a hammerhead structure, suggesting a possible involvement of this in vitro reaction in the in vivo replication mechanism of ASBVd.