DNA-dependent RNA polymerase A (or I) was purified from murine myeloma MOPC 21 by diethylaminoethyl Sephadex chromatography. Further separation from DNA polymerases, protein kinase, and DNA endonuclease was accomplished by polyriboadenylate-Sepharose affinity chromatography followed by gradient centrifugation. Yields following chromatography were 100%, but following gradient centrifugation only 25 to 30% of the activity remained. Addition of low-molecular-weight components increased yields to 50 to 60%. Several species of myeloma polymerase A could be detected, and subunits of 190,000 and 125,000 daltons were identified. No evidence of phosphorylation of the polymerase was found.

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These studies were supported in part by USPHS Grants CA 13600, GM 13543, and GM 00100.

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