5430

Summary Please note that this antibody detects both unphosphorylated and phosphorylated forms of the protein. When using this antibody in western blot and IP, it recognizes both the II0 and IIA form of RPB1 (ie the largest RNAPII subunit). These different forms of RPB1 (as seen in gels) have traditionally been loosely defined as 'hyper-' and 'hypo-phosphorylated', respectively. Here, however, it is important to remember that RPB1 contains no less than 52 repeats of a heptapeptide (TSPTSPS) that can be phosphorylated at different positions (Tyr1, Ser2, Thr4, Ser5 and Ser7; this antibody was raised against a synthetic peptide with 10 of these repeats, mostly but probably not entirely, chemically phosphorylated at Ser5). So, when we say that it recognizes both forms (II0/hyper-phos and IIA/hypo-phos), it might really just mean that the antibody recognizes a few phosphorylated Ser5s among 52 otherwise mostly un-phosphorylated repeats. Alternatively, it might conceivably (though less likely) recognize UN-phosphorylated repeats as there might conceivably be a few of those even in the II0/hyper-phos RPB1 form.