Analysis of Rev protein expression and function in mammalian cells. Rev function was examined by co-transfection of CEM cells with pcDNA3.1-Rev plasmid and the Rev-dependent pDM128 CAT expression plasmid , as described in Materials and Methods. Cells co-transfected with pDM128 and pcDNA3.1 expressing HIV-1NL4-3 Matrix protein or empty pcDNA3.1 vector were included as negative controls. Rev protein expression was determined by Western blotting with sheep anti-Rev polyclonal antisera (A). CAT activity in cell lysates was quantified and normalized to CAT activity in lysates of CEM cells co-transfected with pDM128 and NL4-3 Rev (B). Values shown are means of triplicate transfections. Error bars represent standard deviations. Results are representative of three independent experiments. *P < 0.01, Student's t test.