Beschreibung:
<jats:p>The ubiquitin processing protease, UbpA (a homolog of yeast Ubp14 and human IsoT/USP5), is required for the growth‐to‐development transition of <jats:italic>Dictyostelium</jats:italic>. When <jats:italic>ubpA</jats:italic>¯ cells starve, they accumulate ubiquitin‐containing species that likely include ubiquitin conjugates of proteins that must be degraded for the growth‐to‐development transition to occur. In previous work, we tentatively identified these proteins by S5a‐affinity chromatography and MuDPIT mass spec analysis. Among the putative ubiquitin conjugates was PsmC5. Here we report that a ubiquitination assay showed that his‐tagged PsmC5 is ubiquitinated in lysate prepared from starving cells. In other experiments, we have shown that UbpA is required for the growth‐stage expression of <jats:italic>lmcA</jats:italic>, which is involved in sensing nutrient levels and signaling cells to develop upon starvation. Overexpression of <jats:italic>lmcA</jats:italic> partially rescues the defect in <jats:italic>ubpA¯</jats:italic> cells, suggesting that the <jats:italic>ubpA¯</jats:italic> phenotype is at least partially due to the absence of LmcA. To identify interacting partners of LmcA and elucidate LmcA‐dependent pathways, we purified TAP‐tagged LmcA expressed in <jats:italic>Dictyostelium</jats:italic>. When the putative LmcA‐interacting proteins were further purified by S5a‐affinity chromatography, PsmC5 was recovered, suggesting that ubiquitinated PsmC5 interacts with LmcA. These results will lead to a better understanding of the mechanisms cells use to sense starvation stress and respond by making the transition from growth to development.</jats:p>