SEPARATION AND CHARACTERIZATION OF 2 RELATED GIARDIAVIRUSES IN THE PARASITIC PROTOZOAN GIARDIA-LAMBLIA

Giardiavirus encapsidates a 6.2-kb double-stranded (ds) RNA within a c apsid that consists of a major 100-kDa capsid protein (p100) and a min or 190-kDa protein (p190). In this study, two nonhomologous 6.2-kb ds RNAs cohabiting in Giardia lamblia trophozoites were found to be separ ately encapsidated into two distinct virions, one (designated GLV[p100 ]) whose capsid consists of p100 and p190, and the other (designated G LV[p95]) whose capsid consists of a 95-kDa protein (p95) and a minor p 190-equivalent protein. Both types of virions were enriched in the mem branous fraction of a lysate from virus-infected G. lamblia cells. Sep aration of these virions was achieved by CsCl gradient centrifugation following osmotic rupture of the viral particles. By these treatments, the 6.2-kb ds RNA was removed from GLV[p100] whereas that in GLV[p95] remained unchanged, and the two 6.2-kb ds RNAs that had been purified by this protocol displayed differential hybridization properties to v iral cDNA probes. Western blotting and peptide mapping experiments sho w that p100 and p95 were closely related proteins, but each had distin ct amino acid sequences. Virus purification and pulse-chase experiment s show that GLV[p100] was selectively secreted into the medium whereas GLV[p95] remained within the trophozoites of G. lamblia toward the la te phase of cell growth. Secretion of GLV[p100] was not inhibited by B refeldin A. These findings demonstrate the cohabitation of multiple Gi ardiavirus species in G. lamblia. (C) 1996 Academic Press, Inc.