Molecular cloning and characterization of MSRV-related sequences associated with retrovirus-like particles

New sequences have been obtained by successive overlapping RT-PCR extension s from the pol region of a retroviral RNA (multiple sclerosis-associated re troviral element, MSRV) amplified in retrovirus-like particles from patient s with multiple sclerosis. gag and pol sequences are related to type C onco viruses, whereas the env sequence is closer to type D. A tryptophan-like (W ) tRNA primer-binding site was identified downstream of the RU5 region in t he 5'LTR, and the U3R region cloned in the 3'LTR exhibited potent promoter activity. MSRV clones define a novel family of endogenous elements, HERV-W. From our data, HERV-W RNAs are copackaged in extracellular particles which might be produced by replication-competent or transcomplemented HERV-W cop ies or by an exogenous member of the HERV-W family. (C) 1999 Academic Press .