[Phosphorylation of the ribosomal protein S6 during maturation of Xenopus oocytes: identification of the phosphorylated amino acids].

The S6 protein from the small subunit of Xenopus oocytes in phosphorylated during progesterone-induced maturation. The identity of the amino acids phosphorylated in the S6 protein during this process has been established by two-dimensional electrophoresis followed by radioautography. The only phosphorylated amino acid we could detect is phosphoserine.