We have isolated several genes expressed at abnormal levels in the memory mutant, dunce (dnc), of Drosophila melanogaster. These mutants have an elevated cyclic AMP (cAMP) content due to a mutation in the structural gene for cAMP phosphodiesterase, so the isolated genes are potentially ones regulated by cAMP. Here, we describe the characterization of a genomic clone and corresponding cDNA clones which contain sequences that are underexpressed in dnc mutants. Sequence analysis of portions of the genomic clone and representative cDNAs revealed the presence of two uninterrupted and complete open reading frames (SER1 and SER2) and part of a third (SER3). The predicted amino acid sequences of all of these were found to be homologous to the serine protease family of enzymes. The genomic clone was localized to the polytene chromosome region 99C-D, although genome-blotting experiments indicated the existence of several other genes related to the cloned serine protease-like genes. Hybridization experiments with probes representing each of the three sequenced genes showed that only the SERl-related genes were differentially expressed in dnc mutants. The putative serine protease genes were abundantly expressed in the larval gut, suggesting a major function in digestion. Feeding normal flies cAMP, isobutylmethylxanthine, or forskolin resulted in a decreased RNA level of the SERl-related genes. Thus, RNA levels of this serine protease gene family are negatively regulated by cAMP.Cyclic AMP (cAMP) has been shown to mediate many biological processes in diverse organisms. In procaryotes, cAMP and its receptor protein, CRP, modulate the transcriptional activity of a variety of genes (2). In eucaryotes, the molecule serves as an intracellular second messenger of external stimuli, including hormones and neurotransmitters. One important area of cAMP action currently under intensive study is its role in eucaryotic gene expression. cAMP has been shown, for example, to regulate the mRNA levels of the genes encoding the hormones preproenkephalin (10), gonadotropin (23), prolactin (34), somatostatin (36), vasoactive intestinal polypeptide (44), and growth hormone (47). The mRNA levels of these genes are regulated in a positive manner at least partly at the level of transcription. The RNA of the proto-oncogenes c-myc and c-fos can also be induced by increases in cAMP (5,19,38,43). Genes coding for key metabolic enzymes, including tyrosine aminotransferase, lactate dehydrogenase, tryosine hydroxylase, phosphoenol pyruvate carboxykinase, and dihydrofolate reductase (21,25,32,41,45,50), are regulated at the level of transcription by cAMP in either a positive or a negative way. In addition, the mRNA levels of tubulin and actin, the main protein constituents of microtubules and microfilaments, are modulated by cAMP (16). Thus, cAMP modulates the activity of various genes by altering mRNA abundance, either positively or negatively, and in most cases this modulation occurs at least in part at the level of transcription. The * Corresponding auth...

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.