Involved in protein ubiquitination and degradation during development. Mediates protein ubiquitination at the mound and finger stage required for subsequent development and may be an essential component of the developmental transition between the induction of postaggregative gene expression and subsequent cell-type differentiation and morphogenesis. ubcB and ubpB differentially control ubiquitination/deubiquitination and degradation of mkkA protein in a cell-type-specific and temporally regulated manner. S-ubiquitinyl-[E1 ubiquitin-activating enzyme]-L-cysteine + [E2 ubiquitin-conjugating enzyme]-L-cysteine = [E1 ubiquitin-activating enzyme]-L-cysteine + S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine. Protein modification; protein ubiquitination. Interacts with mkkA (via F-box/WD40 repeat domains). The developmental pattern of protein ubiquitination is altered in null cells. Null cells are blocked in the ability to properly execute the developmental transition that occurs between the induction of postaggregative gene expression during mound formation and the induction of cell-type differentiation and subsequent morphogenesis. Null cells plated on agar form mounds with normal kinetics; however, they remain at this stage for 10 hours before forming multiple tips and fingers that then arrest. Postaggregative gene transcripts accumulate to very high levels and do not decrease significantly with time as they do in wild-type cells. Expression of cell-type-specific genes is very delayed, with the level of prespore-specific gene expression being significantly reduced compared with that in wild-type cells. Defect in the ability of null cells to participate in normal development in chimeras containing wild-type cells. Increased stablity of mkkA and similar phenotype (significant delay at the mound stage and arrest at the first finger stage) of cells that overexpress mkkA. Belongs to the ubiquitin-conjugating enzyme family.