cORF and RcRE, the Rev/Rex and RRE/RxRE homologues of the the human endogenous retrovirus family HTDV/HERV-K

cORF, a protein encoded by the human endogenous retrovirus family HTDV/HERV -K, contains amino acid motifs which resemble the nuclear import and export signals of the viral regulatory proteins Rev (human immunodeficiency virus ) and Rex (human T-cell leukemia virus [HTLV]). In this study, me demonstra ted that cORF indeed has a Rev-like function and mapped the cORF-responsive RNA element to a sequence in the 3' long terminal repeat, a localization s imilar to RxRE, the responsive element in HTLV type 1. Accordingly, me have given the element the designation RcRE. cORF and RcRE stabilize unspliced and incompletely spliced viral transcripts and enhance their nuclear export via the CRM1 export pathway. So far, HTDV/HERV-K is the only endogenous re trovirus family with a complex regulation at the posttranscriptional level. It may be regarded as an intermediate in the evolution from simple to comp lex retroviruses.