Alpha4 protein as a common regulator of type 2A-related serine/threonine protein phosphatases

The catalytic activity of the C subunit of serine/threonine phosphatase 2A is regulated by the association with A (PR65) and B subunits. It has been r eported that the alpha4 protein, a yeast homolog of the Tap42 protein, bind s the C subunit of serine/threonine phosphatase 2A and protein phosphatase 2A-related protein phosphatases such as protein phosphatase 4 and protein p hosphatase 6. In the present study, we showed that alpha4 binds these three phosphatases and the association of alpha4 reduces the activities of these phosphatases in vitro. In contrast, PR65 binds to the C subunit of serine/ threonine phosphatase 2A but not to protein phosphatase 4 and protein phosp hatase 6. These results suggest that the alpha4 protein is a common regulat or of the C subunit of serine/threonine phosphatase 2A and protein phosphat ase 2A-related protein phosphatases. (C) 1999 Federation of European Bioche mical Societies.