SACCHAROMYCES-CEREVISIAE L-BC DOUBLE-STRANDED-RNA VIRUS REPLICASE RECOGNIZES THE L-A POSITIVE-STRAND RNA 3'-END

L-A and L-BC are two double-stranded RNA viruses present in almost all strains of Saccharomyces cervisiae. L-A, the major species, has been extensively characterized with in vitro systems established, but littl e is known about L-BC, Here we report in vitro template-dependent tran scription, replication, and RNA recognition activities of L-BC. The L- BC replicase activity converts positive, single stranded RNA to double -stranded RNA by synthesis of the complementary RNA strand, Although L -A and L-BC do not interact in vivo, in vitro L-BC virions can replica te the positive, single-stranded RNA of L-A and its satellite, M(1), w ith the same 3' end sequence and stem-loop requirements shown by L-A v irions for its own template, However, the L-BC virions do not recogniz e the internal replication enhancer of the L-A positive strand. In a d irect comparison of L-A and L-BC virions, each preferentially recogniz es its own RNA for binding, replication, and transcription, These resu lts suggest a close evolutionary relation of these two viruses, consis tent with their RNA-dependent RNA polymerase sequence similarities.