Uracil-Induced Down-Regulation of the Yeast Uracil Permease

Abstract

In Saccharomyces cerevisiae theFUR4-encoded uracil permease catalyzes the first step of the pyrimidine salvage pathway. The availability of uracil has a negative regulatory effect upon its own transport. Uracil causes a decrease in the level of uracil permease, partly by decreasing theFUR4 mRNA level in a promoter-independent fashion, probably by increasing its instability. Uracil entry also triggers more rapid degradation of the existing permease by promoting high efficiency of ubiquitination of the permease that signals its internalization. A direct binding of intracellular uracil to the permease is possibly involved in this feedback regulation, as the behavior of the permease is similar in mutant cells unable to convert intracellular uracil into UMP. We used cells impaired in the ubiquitination step to show that the addition of uracil produces rapid inhibition of uracil transport. This may be the first response prior to the removal of the permease from the plasma membrane. Similar down-regulation of uracil uptake, involving several processes, was observed under adverse conditions mainly corresponding to a decrease in the cellular content of ribosomes. These results suggest that uracil of exogenous or catabolic origin down-regulates the cognate permease to prevent buildup of excess intracellular uracil-derived nucleotides.

Quality Control and Substrate‐Dependent Downregulation of the Nutrient Transporter Fur4

“…High substrate concentrations increase the turnover rate of transporters, whereas low substrate availability result in stabilization of the transporters. Previous studies found that the substrate-binding site in Fur4 is required for uracilinduced downregulation, suggesting that Fur4 itself is sensing the presence of uracil, thereby regulating its own turnover rate (2). Furthermore, we found that the presence of both extracelluar as well as intracellular substrate is able to induce internalization and degradation of Fur4 (Figure 3), suggesting that any substratebound state is able to trigger Fur4 ubiquitination.…”

Membrane potential governs lateral segregation of plasma membrane proteins and lipids in yeast

“…The number and positions of the MCC patches were shown to be stable (Malinska et al, 2003) and independent of the main cytoskeletal components (Malinska et al, 2004). However, the expression of proteins like Can1p, Fur4p or Tat2p, and consequently their appearance in the plasma membrane, is substrate-regulated (Seron et al, 1999;Kodama et al, 2002). Therefore, these proteins appear in the patches in different amounts and at different times.…”

Arrestin‐Mediated Endocytosis of Yeast Plasma Membrane Transporters

“…We next examined the uracil permease Fur4. This protein has been extensively studied, and it has been shown that the addition of uracil leads to rapid internalization from the cell surface (18). Fur4 is also very sensitive to cycloheximide stress, which similarly results in internalization and vacuolar degradation (19).…”