Characterization of ribonucleoprotein complexes containing an abundant polyadenylated nuclear RNA encoded by Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8)

Infection with Kaposi's sarcoma-associated herpesvirus (KSHV) (also called human herpesvirus 8) is strongly linked to all forms of Kaposi's sarcoma. We have previously identified two polyadenylated KSHV transcripts that are actively transcribed in Kaposi's sarcoma (KS) tumors and in KSHV-infected B-lymphoma cells. One of these RNAs (termed T1.1 or nut-1 RNA) is a 1.1-kb transcript present in a subpopulation of KS tumor cells. This RNA is localized to the nucleus of infected cells and has no open reading frames longer than 62 codons, suggesting that it may not function as an mRNA in vivo. Here we demonstrate that nut-1 RNA is a lytic-cycle gene product that is found in high-molecular-weight ribonucleoprotein complexes in infected cell nuclei. The transcript lacks the trimethylguanosine (TMG) cap found in many U-like small nuclear RNAs, but a subpopulation of nut-1 RNAs can associate with Sm protein-containing small nuclear ribonucleoproteins, as judged by immunoprecipitation analyses using monoclonal anti-Sm and anti-TMG antibodies. This interaction does not require other viral gene products, and deletion of the sole candidate Sm binding site on nut-1 RNA does not ablate this association. This finding suggests an indirect interaction with Sm-containing structures, and models for such associations are presented.