Effect of Sam68ΔC mutants on protein expression from the HIV-1 provirus. 293T cells were transfected with the proviral clone pHxBruR-/RI- in the absence (pcDNA) or presence of the various Sam68ΔC mutants. Western blots on total cell lysates harvested from 293T cells transfected with HxBruR-/RI- and either pcDNA, Sam68ΔC or mutants thereof. p24 is expressed from the 9 kb, gp120 is expressed from the 4 kb, and Rev (top band) is expressed from the 2 kb class of proviral mRNA. Blots were reprobed with anti-myc to confirm protein expression and anti-tubulin to normalize for loading.