EXPRESSION AND BIOCHEMICAL-PROPERTIES OF A PROTEIN-SERINE THREONINE PHOSPHATASE ENCODED BY BACTERIOPHAGE-LAMBDA

The predicted amino acid sequence encoded by the open reading frame 221 (orf221) of bacteriophage lambda exhibited a high degree of similarity to the catalytic subunits of a variety of protein serine/threonine phosphatases belonging to PP1, PP2A, and PP2B groups. Cloning and expression of the orf221 gene in Escherichia coli provided direct evidence that the gene codes for a protein serine/threonine phosphatase. The single-subunit recombinant enzyme was purified in soluble form and shown to possess a unique repertoire of biochemical properties-e.g., an absolute requirement for Mn2+, resistance to okadaic acid, inhibitors 1 and 2, and ability to dephosphorylate casein, adenovirus E1A proteins, and the a subunit of phosphorylase kinase. No phosphotyrosine phosphatase activity was observed. Mutational and biochemical analyses identified the conserved residues 73-77 and Cys138 to be important for activity. The name PP-lambda is proposed for this unusual prokaryotic enzyme.