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-19'. 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. Inhibits the activity of B-type cyclins in replication initiation strongly for CLB2, moderately for CLB3 and CLB4, and there is no apparent inhibition for CLB5 and CLB6, correlating with the normal expression timing of those cyclins. Hyperphosphorylation and degradation of SWE1 when all checkpoint requirement are met releases CLB2-CDC28 from inhibition and allows for progression through the cell cycle. SWE1-dependent CDC28 phosphorylation is also required for pachytene arrest upon activation of the recombination checkpoint during meiosis. Also involved in the regulation of nitrogen starvation- and short chain alcohol-induced filamentous growth, or filamentous differentiation in response to slowed DNA synthesis. Can act both on serines and on tyrosines. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with CLB2-CDC28. Partial hyperphosphorylation of SWE1 by CLB2-CDC28 stabilizes the ternary complex of SWE1 and CLB2-CDC28 and stimulates kinase activity of SWE1 in a positive feedback loop, maintaining CLB2-CDC28 in the tyrosine-phosphorylated state. Fully hyperphosphorylated SWE1 dissociates from CLB2-CDC28. Interacts with HSL7, KCC4 and MET30. When SWE1 first accumulates in G1, it is localized to the nucleus. After bud emergence, a subpopulation is recruited to the daughter side of the mother-bud neck through HSL1 and its adapter HSL7, where it is susceptible to hyperphosphorylation and degradation. Expressed periodically during the cell cycle, with a peak in late G1. Transcriptional repression requires ZDS1. Protein accumulation is also periodic, peaking during S/G2 and declining prior to and during nuclear division of the unperturbed cell cycle. Stabilized during a checkpoint response in G2. Induced during meiosis. Induced by ethanol (at protein level). Ubiquitinated by the SCF(MET30) complex, leading to its degradation by the proteasome. Phosphorylated progressively by CLA4, CLB2-CDC28 and CDC5. CLA4-dependent phosphorylation occurs in late S phase, followed by phosphorylation by CLB2-CDC28 in early G2, when the levels of mitotic CLB2 increases. This phosphorylation is critical for triggering subsequent SWE1-CDC5 interaction and CDC5-dependent phosphorylation. The resulting cumulative hyperphosphorylation down-regulates SWE1 by targeting it for ubiquitin-mediated degradation. This stepwise phosphorylation is thought to be a mechanism to integrate the different checkpoint requirements before entry into mitosis. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. WEE1 subfamily.