The mitochondrial glycine cleavage complex has an important role in metabolism since it provides the cell with the ability to use glycine as sole one-carbon and sole nitrogen source. In previous studies we have found that the genes encoding the unique components of this complex (GCV1, GCV2 and GCV3) are regulated by the one-carbon status of the cell. Here we have examined the transcriptional regulation of these genes with respect to nitrogen source. Two controls are required for the full range of GCV2 expression. One acts through a GATA sequence known to be involved in the control of transcription in response to the quality of the available nitrogen source and the other acts through an eight-base palindrome immediately 5' of the GATA element. This palindromic sequence previously had no known function. These data expand the repertoire of nitrogen catabolite repression to include the poor nitrogen source glycine and the genes encoding the enzyme complex responsible for its catabolism. Furthermore, deletion analyses and mutagenesis have shown that the palindromic sequence is important for full repression of GCV2 in complex glucose-containing medium and functions in a manner that is different from control mediated by the GATA element.