Pest sequences present in the subunits of phosphorylase kinase

We report that the amino acid sequences of all four subunits of rabbit skeletal muscle phosphorylase kinase possess one or more regions rich in proline (P), glutamic acid (E), serine (S) and threonine (T). alpha and beta subunits contain strong PEST sequences, showing PEST scores greater than 0 (Rogers et al. (1986) Science 234, 364-368), while gamma and delta subunits contain weak PEST regions (negative PEST scores greater than -5.3). In addition to PEST sequences, alpha, beta and gamma subunits contain clusters of arginine pairs. The above sequence characteristics may serve to signal rapid turnover of phosphorylase kinase.