Fig. 2. Interactions between the different machineries. Various antibodies (A-C) or proteins (D) bound to beads were incubated with HeLa nuclear extract, and proteins immunoprecipitating (IP) with bound antibodies or proteins analysed by immunoblotting. ^aNormal mouse serum; ^b1/5 extract used for IP applied directly to lane; ^cbeads coated with anti-biotin, and extract from permeabilized cells containing nascent peptides tagged without (`control') and with biotin (`bio-peptide'); ^d1/10 extract used for IP applied directly to lane; ^ebeads coated with anti-Br, and extract from permeabilized cells containing nascent transcripts tagged without (`control') and with bromine (`Br-RNA'); ^fextract from permeabilized cells containing nascent Br-RNA. (A) CTD^P co-immunoprecipitates with another subunit of the polymerase (RPB8), translation initiation factors (left), NMD proteins (middle) and nascent biotin-peptides (right). (B) CTD^P and NMD proteins co-immunoprecipitate with proteins in ribosomes and newly made transcripts, but not histone H4. (C) Components involved in NMD (left) and translation (right) co-imunoprecipitate with nascent Br-RNA and RPB8. (D) The CTD interacts with S6 and UPF1, but not VP16.