Clones carrying sequences expressed at altered abundance levels in dunce mutants were isolated by differentially screening a genomic library with cDNA probes representing the RNA population from dunce+ flies and the RNA population from dunce mutant flies. These mutants have an elevated cAMP content, so some isolates potentially contain cAMP responsive genes. Two classes of clones were isolated. One class contains genes expressed at a higher steady state abundance level in dunce mutants compared to dunce+ flies and the other contains genes expressed at a lower steady state level in the mutants. The recovery of clones from the differential screen demonstrates that in addition to altering normal behavior, fertility, and cAMP metabolism, dunce mutation confers an alteration in the level of expression of certain genes. The class of clones carrying sequences which are overexpressed in the mutants have been characterized. These clones carry a common repetitive sequence which codes for a 5.5 kb poly(A)+ RNA - the RNA species found to be overexpressed in the mutants. Restriction analysis and hybridization experiments show these repetitive sequences to be members of the copia family of transposable elements. Administration of pharmacological agents to normal flies to increase cAMP levels leads to an increased steady state level of copia RNA. Thus, copia RNA metabolism appears to be influenced by cAMP levels.