SUMMARY PARAGRAPH for FUI1
Fui1p is a uridine permease located in the plasma membrane. It has high affinity and selectivity for uridine (3, 1, 2), and does not transport uracil or allantoin into the cell (6, 2).
fui1 null mutants are viable, and are resistant to 5-fluorouridine, but do not grow on medium containing uridine as the sole source of pyrimidines (7, 2, 1). In a large-scale synthetic genetic array analysis, fui1 mutations also cause synthetic growth defects in combination with mutations in either LAS21, which encodes a plasma membrane protein involved in glycosylphosphatidylinositol synthesis, or RIC1, which encodes a protein involved in retrograde transport to the cis-Golgi network (8). Fui1p is able to transport uracil when it is overexpressed, and overexpression of Fui1p results in a decreased growth rate in the presence of uridine (2, 6).
Fui1p is degraded via ubiquitination, endocytosis, and then vacuolar degradation (9, 6). Uridine promotes Rsp5p-dependent ubiquitination of Fui1p at the plasma membrane, followed by its endocytosis and then vacuolar degradation (6). In cells being exposed to toxic levels of uridine, uridine is also able to direct Fui1p for early vacuolar degradation immediately after synthesis, without prior localization of Fui1p to the plasma membrane (6).
FUI1 belongs to a family of uracil/uridine/allantoin permease homologs, and has similarity to DAL4, FUR4, THI7, and YOR071C, and Schizosaccharomyces pombe fur4 (10, 11, 12, 2, 13, 14).
Last updated: 2005-12-14