THE OPEN READING FRAME-I (ORF-I) ORF-II PART OF THE HUMAN T-CELL LEUKEMIA-VIRUS TYPE-I X-REGION IS DISPENSABLE FOR P40(TAX), P27(REX), OR ENVELOPE EXPRESSION/

The X region of the human T-cell leukemia virus type I contains the se cond coding exon of the tax and rex regulatory proteins (open reading frame IV ORF IV and ORF III, respectively), as well as coding region s for Ir more recently described proteins, p30(II) (or the tof protein ) and p13(II) in ORF II and the putative rof protein and p12(I) in ORF I. Deletions and transcomplementation experiments showed that express ion of the envelope, as well as that of the tax and rex proteins, was independent of the proteins encoded in the ORF I/ORF II region. Furthe rmore, p30(II) and p12(I) proteins could not replace the rex protein i n a rex-dependent envelope or Gag protein expression system.