Molecular data rapidly accumulating on the regulation of gene expression by amino acids in mammalian cells highlight the large variety of mecha-nisms that are involved. Transcription factors, such as the basic-leucine zipper factors, activating transcription factors and CCAAT/enhancer-bind-ing protein, as well as specific regulatory sequences, such as amino acid response element and nutrient-sensing response element, have been shown to mediate the inhibitory effect of some amino acids.
