Memory formation after olfactory learning in Drosophila displays behavioral and molecular properties similar to those of other species. Particularly, long-term memory requires CREB-dependent transcription, suggesting the regulation of "downstream" genes. At the cellular level, long-lasting synaptic plasticity in many species also appears to depend on CREB-mediated gene transcription and subsequent structural and functional modification of relevant synapses. To date, little is known about the molecular-genetic mechanisms that contribute to this process during memory formation.We used two complementary strategies to identify these genes. From DNA microarrays, we identified 42 candidate memory genes that appear to be transcriptionally regulated in normal flies during memory formation. Via mutagenesis, we have independently identified 60 mutants with defective long-term memory and have defined molecular lesions for 58 of these. The pumilio translational repressor was found from both approaches, along with six additional genes with established roles in local control of mRNA translation. In vivo disruptions of four genes--staufen, pumilio, oskar, and eIF-5C--yield defective memory.Convergent findings from our behavioral screen for memory mutants and DNA microarray analysis of transcriptional responses during memory formation in normal animals suggest the involvement of the pumilio/staufen pathway in memory. Behavioral experiments confirm a role for this pathway and suggest a molecular mechanism for synapse-specific modification.