Localization of the replicase recognition site within brome mosaic virus RNA by hybrid-arrested RNA synthesis.

3' terminal fragments of BMV RNA as short as 153 bases in length serve as efficient templates in vitro for BMV-specific RNA polymerase. Template activity of such fragments or of native BMV RNA is abolished when cDNA fragments as short as 39 bases are hybridized to their 3' termini. Hybridization of cDNa fragments to regions of BMV RNA 200 or more bases distal to the 3' end has no discernible effect on initiation and little effect on elongation. We conclude that BMV RNA polymerase initiates binding with an RNA template through a mechanism mediated by the tRNA-like 3' end of BMV RNA, requiring at least some of the last 39, but no more than the last 153 bases.