SUPPRESSION OF LEISHMANIA RNA VIRUS-REPLICATION BY CAPSID PROTEIN OVEREXPRESSION

Some strains of the protozoan parasite genus Leishmania are persistent ly infected with single-segmented double-stranded RNA viruses, which a re termed LRV. The function of these cytoplasmic viruses is unknown. I n order to address the question of whether LRV affects the parasite's phenotype, pairs of isogenic LRV(+)-LRV(-) lines are required. Since t he persistent nature of these viruses precludes de novo infection of v irus-negative strains, LRV(+)-LRV(-) strains were transformed with a L eishmania expression vector expressing the LRV capsid protein with the aim of determining if LRV(-) promastigotes support capsid assembly an d if LRV replication is affected by excess capsid protein. I found tha t in LRV(-) promastigotes, capsid protein was capable of self-assembly into virus-like capsids and that capsid overexpression in a naturally infected LRV(+) line resulted in a progressive reduction in LRV copy number. Clonal lines derived from an LRV(+) capsid overexpressor had n o detectable levels of LRV. These results demonstrate that LRV replica tion can be inhibited and that a significant reduction of viral copy n umber has no effect on the parasite's viability in liquid medium.