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Coexpression of mutant and wild type protein kinase in lymphoma cells resistant to dibutyryl cyclic AMP

A mutant clone resistnat to dibutyryl cyclic AMP was isolated from S49 mouse lymphoma cells. The mutant expressed a form of cyclic AMP‐dependent protein kinase distinguishable from wild type kinase by its decreased sensitivity to activation by cyclic AMP and its increased thermal lability. Hybrids formed between mutant and wild type cells were resistant to dibutyryl cyclic AMP and expresed both mutant and wild type activities in about equal amount. The parent mutant cells also appeared to express wild type kinase activity, but at a lower level. We conclude that wild type S49 cells have and expression two identical alleles for the regulatory subunit of protein kinase, one of which has undergone mutation in the mutant cells.