Yeast cells exhibit sustained ultradian oscillations of energy metabolism in coupling with cell cycle and stress resistance oscillations in continuous culture. We have reported that the rhythmic expression of Gts1p is important for the maintenance of ultradian rhythms. Structurally, Gts1p contains sequence motifs similar to N-degron and the ubiquitin association domain, raising the possibility that the Gts1p level is regulated by degradation via ubiquitination. When the lysine residue at the putative ubiquitination site of the N-degron was substituted with arginine, both the protein level and half-life of mutant Gts1p increased. During continuous culture, the protein level of the mutant Gts1p was elevated and did not fluctuate, leading to the disappearance of metabolic oscillation within a day. Furthermore, using three Gts1ps containing mutations in the ubiquitin association domain, we showed that the lower the binding activity of the mutant Gts1ps for polyubiquitin in vitro, the higher the protein level in vivo. Expression of the mutant Gts1ps in the continuous culture resulted in an increase in Gts1p and early loss of the oscillation. Therefore, Gts1p is degraded through conjugation with ubiquitin, and the UBA domain promoted the degradation of ubiquitinated Gts1p, causing a fluctuation in protein level, which is required for the maintenance of metabolic oscillations.In an open system using a bioreactor, yeast cells exhibit sustained ultradian oscillations of energy metabolism in a continuous (chemostat) culture under aerobic and glucose-limited conditions (1-4). The energy metabolism pathway has been proven to be an autogenous oscillator under extreme nonequilibrium energy conditions according to the theory of "dissipative structures" established by Prigogine and others (5-7). In brief, the metabolic pathway oscillates autonomously under the primary control of phosphofructokinase, transferring energy from glucose to NADH, which acts as the feed-forward activator, and then from NADH to ATP, which acts as the feedback inhibitor. After ATP as an inhibitor is consumed as fuel for various ATPases, glucose again begins to enter the glycolytic pathway. The oscillations are detectable as a periodic change in the factors involved in energy metabolism such as dissolved oxygen (DO) 1 levels, CO 2 production, glucose and ethanol concentrations, and amounts of storage carbohydrates. DO oscillation is due to the periodic change between respiratory and respiro-fermentative phases in which oxygen demands are relatively high and low, respectively. DO oscillations arise spontaneously in concert with cell division and are dependent on a high cell density (ϳ5 ϫ 10 8 cells/ml), regulating the cell density throughout the oscillation (8). We have reported that cellular responses to various stress conditions, such as heat, oxidative agents, and cytotoxic compounds, are regulated in concert with metabolic oscillation (8) and that the coupling 2 was disrupted by inactivation of the GTS1 gene (9). Furthermore, we suggested that the rhy...