On the role of protein kinase subunits in the control of eukaryotic gene expression

Transcriptional regulation by cAMP has been demonstrated for several eukaryotic genes; however, the identity of the protein kinase subunit involved has been a source of debate. Based on homologies with the procaryotic cAMP-binding catabolite activator protein, a recent hypothesis has invoked the regulatory protein RII as the mediator. The evidence currently available on the effects of microinjected kinase subunits suggests, however, that the catalytic subunit is the active factor. Moreover, the proposed homologies between the catabolite activator protein and RII are difficult to reconcile with its proposed mediatory role. We suggest as an alternative hypothesis that a phosphoprotein other than RII may mediate the effects of cAMP on eukaryotic gene expression.