Genomic structure and RNA polymerase activity in Leishmania virus

Viral particles infecting some stocks of the protozoan parasite Leishmania braziliensis subsp. guyanensis contain a double-stranded RNA genome of ca. 5 kbp and are associated with an RNA-dependent RNA polymerase which synthesizes in vitro double-stranded and single-stranded, genome-length transcripts. The majority of viral transcripts are single-stranded and templated from one genomic strand. The putative replicase generates double-stranded RNA by synthesizing the opposite strand on a preexisting RNA template. These data are compatible with a replicative cycle proposed for the yeast viruses. Purification of the Leishmania virus on CsCl yields virus without double-strand synthesis activity, while this activity is consistently present in unpurified virus and in particles from sucrose gradients. The deficiency in double-strand synthesis in CsCl-derived virions correlates with the accessibility of the viral polymerase and genomic RNA to exogenously added enzymes, indicative of a structural modification of the viral capsid.