Dephosphorylation of cytoplasmic non-polysomal messenger ribonucleoproteins from cryptobiotic gastrulae of Artemia salina.

Cytoplasmic non-polysomal mRNP from cryptobiotic gastrulae of the brine shrimp Artemia salina do not contain endogeneous protein phosphatase activity. However, both non-polysomal mRNP and purified mRNP proteins, phosphorylated by mRNP associated protein kinase, can be dephosphorylated by protein phosphatases purified from A. salina cytosol and rabbit skeletal muscle. The 38 kDa and 23.5 kDa poly(A) binding proteins (P38 and P23.5) and a 65 kDa protein are the major substrates of each protein phosphatase used. The reversible phosphorylation-dephosphorylation of mRNP may be involved in the regulation of mRNP metabolism, by altering the poly(A) binding capacities of the mRNP proteins.