Fig. 4. Reduced MyoD mRNA levels in Tax-expressing muscle cells. Total RNAs were isolated from C2.7-Neo (Lanes 1 and 2) and C2.7-Tax (Lanes 3 and 4) cultured in proliferation medium for 48 h (PM; Lanes 1 and 3) or switched to differentiation medium at 80% confluence and cultured for an additional 48 h (DM; Lanes 2 and 4). Twenty µg of each RNA preparation were fractionated in a formaldehyde-agarose gel and transferred to a nylon membrane as described in "Materials and Methods." This membrane was then sequentially hybridized with 32P-labeled Tax, E2A, Id1, Id2, Id3, GAPDH, and MyoD probes and then subjected to autoradiography.