A Monoclonal Antibody Against the PSTAIR Sequence of p34cdc2, Catalytic Subunit of Maturation-Promoting Factor and Key Regulator of the Cell Cycle

A homolog of the serine/threonine protein kinase (p34^cdc2), encoded by the cdc2 ⁺ gene of the fission yeast ( Schizosaccharomyces pombe ), is a catalytic subunit of maturation-promoting factor and a key regulator of the cell cycle. We have raised a monoclonal antibody against the most conserved amino acid sequence, the PSTAIR sequence (EGVPSTAIREISLLKE) of p34^cdc2 This antibody recognizes 31–34 kDa proteins by immunoblotting in all species examined so far. The proteins recognized by the anti-PSTAIR antibody are probably either p34^cdc2 itself or proteins highly homologous to p34^cdc2 in the given species, since, in all species studies to date, they are all precipitated with p13^suc1, the fission yeast suc 1⁺ gene product, which binds to p34^cdc2 with high specificity. The anti-PSTAIR immunoprecipitate had no histone H1 kinase activity and did not contain cyclin B, suggesting that the PSTAIR region is masked when p34^cdc2 forms a complex with cyclin B as an active kinase. Immunoblotting with the anti-PSTAIR antibody demonstrated that the fastest-migrating form of p34^cdc2 homologues becomes abundant, when oocytes mature or the cell enters M phase. The possible significance of this observation is discussed in relation to the phosphorylation and activity state of p34^cdc2 The observed broad cross-reactivity of the anti-PSTAIR antibody against p34^cdc2 homologues in various species should permit us to examine the role of p34^cdc2 homologues in the regulation of the cell cycle in a variety of organisms.