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

Abstract
The structures of 2 protein factors, S-II and S-II'', that specifically stimulate RNA polymerase II from [mouse] Ehrlich ascites tumor cells were compared. The 2 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. S-II and S-II'' gave identical peptide maps when digested with various proteases. 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. S-II'' was phosphorylated more than S-II when Ehrlich ascites tumor cells were labeled in vivo with [32P]orthophosphate.

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