The ubiquitin-proteasome system (UPS) is involved in the degradation of many intracellular proteins and is necessary for a proper functioning of the cell under normal conditions and its survival in stress. This review considers the general principles of the structure and functioning of the UPS. Main attention is paid to the expression regulation of the proteasomal genes in yeasts and structural and functional analyses of the Rpn4p transcription factor, which activates the proteasomal genes in Saccharomyces cerevisiae. Data on the regulation of proteasomal gene expression in higher eukaryotes are discussed.