PTB Binds Specifically to MS HIV-1 RNA and Is Upregulated upon Cellular Stimulation

<div><p>(A) PTB binds specifically to MS HIV-1 RNA. Recombinant PTB was pre-incubated with increasing molar equivalents (0X, 1X, 2X, 5X) of non-biotinylated MS HIV-1 RNA (relative to biotinylated MS HIV-1 RNA) or a 5-fold mass excess of non-specific (NS) competitor, total yeast RNA; and then incubated with biotinylated, in vitro-transcribed MS HIV-1 RNA bound to streptavidin-conjugated magnetic particles. PTB protein eluted by RNase digestion was analyzed by Western blot.</p><p>(B) PTB expression increases in response to T-cell stimulation. Expression of PTB was measured by Western blotting in resting CD4⁺ T cells cultured for 72 h without activating stimuli (−) or with (+) anti-CD3/anti-CD28. Vinculin served as a loading control.</p>