Protein kinase that acts as a negative regulator of entry into mitosis (G2 to M transition) by phosphorylating and inhibiting the mitosis-promoting cyclin B-bound CDC28 at 'Tyr-18'. SWE1-mediated inhibition of CDC28 acts in a cell size or morphogenesis checkpoint to delay mitosis in response to defects in growth, actin organization or bud formation. Plays an important role in filamentous growth. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Phosphorylated. Leads to hypersensitivity to caspofungin. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. WEE1 subfamily.