Adaptation to amino acid deficiency is critical for cell survival. In yeast, this adaptation involves phosphorylation of the translation initiation factor eIF2alpha by the kinase GCN2. This leads to the increased translation of the transcription factor GCN4, which in turn increases transcription of amino acid biosynthetic genes, at a time when expression of most genes decreases. Here it is shown that translation of the arginine/lysine transporter cat-1 mRNA increases during amino acid starvation of mammalian cells. This increase requires both, GCN2 phosphorylation of eIF2alpha and the translation of a 48 amino acid upstream-ORF present within the 5-leader of the transporter mRNA. When this 5-leader was placed in a bicistronic mRNA expression vector, it functioned as an internal ribosomal entry sequence (IRES) and its regulated activity was dependent on upstream-ORF translation. Amino acid starvation also induced translation of monocistronic mRNAs containing the cat-1 5-leader, in a manner dependent on eIF2alpha phosphorylation and translation of the 48 amino acid uORF. This is the first example of mammalian regulation of IRES-mediated translation by eIF2alpha phosphorylation during amino acid starvation, suggesting that the mechanism of induced cat-1 protein synthesis is part of the adaptive response of cells to amino acid limitation.