A yeast DNA fragment complementing the met6 mutation in yeast (Saccharomyces cerevisiae) was cloned in a shuttle vector, Yep13, by transforming a yeast host with plasmid DNA prepared from yeast gene bank CV13 of K. Nasmyth. A restriction map of a 6-kb Sau3A insert was constructed. A 2.6-kb fragment (Sau3A-BamHI) complementing the mutation was found by subcloning. Evidence that the DNA fragment contains the yeast MET6 gene was obtained by genomic integration. A 2.5-kb transcript is found both in wild-type (wt) and met6 yeast strains by Northern blotting experiments, indicating that the mutation acts at posttranscriptional level. The rate of transcription for the integrant lies between the values observed for the wt and mutant strains. The functional gene product seems to be involved in negative regulation of transcription of the MET6 gene.