LOCATION OF CIS-ACTING SIGNALS IMPORTANT FOR RNA ENCAPSIDATION IN THELEADER SEQUENCE OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-2

We used a series of deletion mutations in the untranslated leader regi on of human immunodeficiency virus type 2 (HIV-2) to seek cis-acting p ackaging signals, Sequences between the 5' major splice donor and the gag initiation codon, where such signals have been identified in HIV-1 , appear to make a measurable but very minor contribution to genomic R NA packaging, and deletions here had little effect on viral replicatio n in vitro, Immediately 5' to the splice donor, two regions were ident ified which, when deleted, caused a significant replication defect, Th e most proximal of these to the splice donor demonstrated a phenotype consistent with its being a major cis-acting packaging signal in HIV-2 .