Expression and regulation of the mammalian SUMO‐1 E1 enzyme

SPECIFIC AIMSSUMO-1 E1 enzyme subunits associate as a simple heterodimeric complex, but purified E1 heterodimer plus the E2 enzyme is significantly less efficient than cellular extracts in catalyzing SUMO-1 conjugation, suggesting the existence of previously uncharacterized positive regulators of this reaction. In conjunction with further examination of the expression, localization, and biochemical behavior of SUMO-1 pathway enzymes, these findings suggest that SUMO-1 conjugation may be controlled during the cell cycle by at least two separate mechanisms.PRINCIPAL FINDINGS1. SUMO-1 conjugation varies during the cell cycleAnalysis of three prominent SUMO-1-conjugated species in HeLa cells revealed distinct patterns of abundance in cells synchronized in different parts of the cell cycle (Fig. 1A⤻ ). The 90 kDa species corresponding to RanGAP1-SUMO-1 was roughly constant throughout the cell cycle. The abundance of the conjugated species with an apparent molecular mass of 100 kDa (p100) changed less than twof...