Wee1 is a nuclear tyrosine protein kinase. The protein plays a role in suppressing eukaryotes’ entry into mitosis by inactivating cdc2 kinase by inhibiting tyrosine phosphorylation. The predicted molecular weight of the kinase is 72 kDa. The kinase possesses tyrosine kinase activity, but structurally belongs to the serine/threonine protein kinase family.