FIG. 2.
Immunoprecipitation of UV cross-linked proteins. Cytoplasmic extracts from HeLa (lanes 1 to 4) and DBT (lanes 5 to 8) cells were UV cross-linked with 32P-labeled plus-strand leader RNA; digested with RNase A; and precipitated with monoclonal antibody for PTB (lanes 2 and 6), monoclonal antibody for TFIIB (lanes 3 and 7), or polyclonal antibody for Sam68 (Santa Cruz Biotechnology) (lanes 4 and 8). The precipitated proteins were collected with protein A-Sepharose beads (Zymed) and analyzed by SDS-PAGE. Lanes 1 and 5 are UV cross-linked proteins without immunoprecipitation (IP). Numbers at left show molecular mass in kilodaltons.