A CELLULAR PROTEIN WHICH IS COPRECIPITATED WITH HTLV-I REX PROTEIN INTHE PRESENCE OF THE TARGET MESSENGER-RNA

We examined the cellular protein(s) which can associate with Rex prote in of human T cell leukemia virus type I (HTLV-I), using Rex-maltose b inding protein (MBP) fusion protein. Immunoprecipitation of RexMBP wit h anti-MBP antibody revealed that a 24 kD protein (p24) associated wit h RexMBP only in the presence of Rex-responsive mRNA. The fact that p2 4 was present in both the nucleus and the cytoplasm is consistent with a role of Rex in the nucleo-cytoplasmic transport of viral mRNAs. P24 did not interact with nonfunctional Rex mutant proteins even if they had RNA binding activity in vitro. These results suggest the possible involvement of p24 in the Rex function through a complex formation wit h Rex on Rex-responsive mRNA.