Primary structure of vertebrate somatic Wee1 proteins. The numbering is from human somatic Wee1. The NRD, kinase domain, and short carboxy-terminal domain are marked, with border amino acid residues numbered (below). RxL1 (residues 180-2) is embedded within the Crm1 binding site (175-184). The T239 Cdk phosphorylation site, an inhibitory modification, resides within the Wee box, a positive regulatory element.