Phosphorylation of specific polypeptides in isolated murine splenocyte nuclei which is controlled by cyclic...

Murine splenocyte nuclei were phosphorylated with a less than 10(-5) M concentration of [gamma-32P]ATP at 0 degrees C and the phosphorylated nuclear proteins were analyzed by SDS-polyacrylamide gel slab electrophoresis and Sephadex gel filtration column chromatography. Two polypeptides of 10K and 11K daltons were predominantly phosphorylated. These polypeptides were likely linked by a disulfide bond to form a nonhistone protein of 21K daltons. Both phosphoserine and phosphothreonine were detected in the hydrolysate of the 10.5K dalton polypeptide, while phosphoserine was predominant in the 10K dalton polypeptide. Maximal activation of phosphorylation by cAMP of both polypeptides was shown at a concentration of 10(-6) M. On the contrary, cGMP activated phosphorylation of the 10K dalton polypeptide at 10(-8) M and at 10(-4) M. The phosphorylation of the 10.5K polypeptide was not activated by 10(-4) M cGMP and suppression of the phosphorylation was seen in both polypeptide chains by cAMP at higher concentrations.