Difference in phosphorylation of two factors stimulating RNA polymerase II of Ehrlich ascites tumor cells

The structures of two protein factors, S-II and S-II', that specifically stimulate RNA polymerase II from Ehrlich ascites tumor cells were compared. The two proteins behaved differently on CM-cellulose chromatography and on isoelectric focusing, although they were shown to have common antigenicity. The following findings strongly suggest that S-II and S-II' have the same primary structure, but that S-II' is more extensively phosphorylated than S-II: (1)S-II an S-II' gave identical peptide maps when digested with various proteases. (2) S-II' that had been treated with alkaline phosphatases had the same mobility on sodium dodecyl sulfate-polyacrylamide gel as S-II, indicating that it could be converted to S-II by hydrolysis of its phosphate residues. (3) S-II' was phosphorylated more than S-II when Ehrlich ascites tumor cells were labeled in vivo with [32P]orthophosphate.