Transient expression SF2/ASF in CV1 cells inhibits HIV Rev function. (A) Diagram of the pDM128 plasmid used in these studies. (B) CV1 cells were transfected with the Rev-responsive pDM128 CAT reporter plasmid in the presence and absence of Rev and various amounts of pSF2/ASF expression plasmid. DNA concentration was held constant by the addition of pCMV4 parental plasmid. Forty-eight hours after transfection, the cells were lysed and CAT assays were performed. (C) CV1 cells were transfected with the pDM128–RexRE reporter plasmid in which HIV-1 RRE was replaced by the HTLV-I RexRE. An HTLV-I Rex expression plasmid pcRex was transfected instead of HIV-1 pcRev. (D and E) CV1 cells were transfected with pDM128, HIV-1 Rev, and various amounts of two different SF2/ASF substitution mutants including SF2/ASF-FF-DD altered in the RNP-1 region of the RRM and the SF2-RT, where all serines in the RS domain were replaced with threonine (20). (F) CV1 cells cotransfected with pDM128, HIV-1 Rev, and various amounts of a second SR protein expression vector pSRp40. Stable expression of SF2/ASF FF-DD, SF2/ASF RT, and SRp40 was confirmed by immunoblotting of transfected CV-1 cell lysates.