Mud2 interacts with Prp19C and is recruited to an intronless gene in D. melanogaster. (A) U2AF50, the Drosophila homolog of Mud2, interacts with the Prp19C complex components Prp19 and Fandango, the Drosophila homolog of Syf1. Prp19, Fandango or U2AF50 were immunoprecipitated with antibodies directed against the respective protein and (co-)purification in the immuno precipitate (IP) assessed by Western blotting (left panel). As negative control served TAF3, a subunit of the transcription initiation factor TFIID (left panel). The interactions between U2AF50, Prp19 and Fandango are independent of RNA and DNA as these proteins also copurify, when the extract is treated with RNase and DNase (right panel). (B) U2AF50 interacts with RNAPII in its S2 phosphorylated state in vivo. IP experiment and Western blots as in A using antibodies directed against RNAPII, the S2 phosphorylated CTD and U2AF50. (C) U2AF50, Prp19 and Fandango are recruited to the intronless Hsp70 gene in a transcription-dependent manner. ChIP experiments were performed with antibodies directed against U2AF50, Prp19, Fandango and RNAPII under non-induced (NHS: non-heat shock, dark-gray bars) and induced (HS: heat shock, light-gray bars) conditions. The position of the primer pairs used to determine the co-immunoprecipitated DNA at two positions in the promoter (P1, P2) and four positions in the ORF (M1–M4) of the Hsp70 gene are indicated in the top left panel.