Transcribed regions on a 42-kb segment of chromosome I from Saccharomyces cerevisiae were mapped. Polyadenylated transcripts corresponding to eight previously characterized genes (MAK16, LTE1, CCR4, FUN30, FUN31, TPD3, DEP1, and CYS3) and eight new genes were identified. All transcripts were present at one to four copies per cell except for one which was significantly less abundant. This region has been sequenced, and the sizes, locations, and orientations of the transcripts were in nearly perfect agreement with the open reading frames. Disruptions in eight genes identified solely on the basis of a transcribed region, FUN38, FUN25, FUN26, FUN28, FUN30, FUN31, FUN33, and FUN34, indicated that all were nonessential for growth on rich medium at 30 degrees C. Disruption of FUN30, a gene closely related to RAD16 and RAD54, surprisingly resulted in increased resistance to UV irradiation. No additional phenotypes, other than slow growth, were observed for all other mutants. The distribution of essential genes on chromosome I is discussed.