Multiple nitrocellulose DNA filter replicas of plaques of in vitro generated recombinants of phage lambda and Saccharomyces cerevisiae have been screened by hybridization with 32P-labeled cDNA probes. These probes were representative of total poly(A)-containing RNA of yeast cells grown on acetate, galactose, glucose or maltose. This approach allows the use of specific differences in total RNA populations as probes for gene isolation. Five "galactose-induced" clones have been isolated. Expression of the RNA coding regions on at least two cloned sequences, Sc481 and Sc482, is regulated by genes known to control the expression of the structural genes required for the conversion of exogenous galactose to endogenous glucose-1-phosphate. One cloned sequence, Sc484, is expressed during growth on all carbon sources except glucose, and is not under control by the galactose regulatory genes. This clone contains a sequence that is repeated 3 times in the yeast genome. The cloned fragment Sc481 contains coding regions for all or part of three galactose"induced RNAs and may correspond to the GAL 1, GAL 7, GAL 10 gene cluster region of chromosome II.