In yeast, most amino acid biosynthetic pathways are coregulated: starvation for a single amino acid results in derepression of enzyme activities for many different biosynthetic pathways. This phenomenon is referred to as "general control of amino acid biosynthesis." In this paper we describe the isolation and characterization of 43 amino acid analog-sensitive (aasw) mutants that are perturbed in this general regulatory system. These 43 mutations define four unlinked complementation groups, AAS101, AAS102, AAS103, and AAS104, two of which identify previously unreported genes involved in general control. These aas mutants are unable to derepress a number of amino acid biosynthetic genes, resulting in increased sensitivity to amino acid analogs, reduced growth rates, and reduced enzyme activity levels under amino acid starvation conditions. Thus, the AAS' gene products function as positive regulatory elements for this system. We show that the AAS genes mediate these effects by regulating the mRNA levels of genes under their control.In prokaryotes, functionally related genes are organized into single transcriptional units called operons, the expression of which is controlled by positive or negative elements acting on a single adjacent regulatory region. In eukaryotes, however, functionally related genes are generally scattered on different chromosomes; neither operons nor polycistronic mRNAs have been identified (1-3). Still, coregulation of these unlinked genes occurs, suggesting that regulation is mediated by a mechanism fundamentally different from that used in prokaryotes.