Regulates cell-type differentiation and spatial patterning, required for the proper induction and maintenance of prespore cell differentiation. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with ubcB and ubpB. Localized predominantly at the periphery of the cells, possibly in the cortex or the plasma membrane. ubcB and ubpB differentially control ubiquitination/deubiquitination and degradation in a cell-type-specific and temporally regulated manner. Cells develop precociously and exhibit abnormal cell-type patterning with an increase in the pstO prestalk compartment, a concomitant reduction in the prespore domain, and a loss of the sharp compartment boundaries, resulting in overlapping prestalk and prespore domains. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase kinase subfamily.