MOLECULAR-CLONING AND CHARACTERIZATION OF A TRANSCRIPTION FACTOR FOR THE COPIA RETROTRANSPOSON WITH HOMOLOGY TO THE BTB-CONTAINING LOLA NEUROGENIC FACTOR

By transfection experiments, we previously identified a 72-bp enhancer sequence within the Drosophila copia retrotransposon which is involve d in the control of the transcription level of this mobile element in cells in culture, Gel shift assays with nuclear extracts from Drosophi la hydei-derived DH-33 cells further demonstrated specific interaction s of at least two nuclear factors with this enhancer sequence, Using t his sequence as a probe for the screening of an expression cDNA librar y that we constructed from DH-33 cells RNA we have isolated a cDNA clo ne encoding a 110-kDa protein with features common to those of known t ranscription factors; these include a two zinc-finger motif at the C t erminus, three glutamine-rich domains in the presumptive activation do main of the protein, and an N-terminal domain which shares homology wi th the Bric-a-brac, Tramtrack, and Broad-Complex BTB boxes. The precis e DNA recognition sequence for this transcription factor has been dete rmined by both gel shift assays and footprinting experiments with a re combinant protein made in bacteria. The functionality of the cloned el ement was demonstrated upon transcriptional activation of copia report er genes, as well as of a minimal promoter coupled with the identified target DNA sequence, in cotransfection assays in cells in culture wit h an expression vector for the cloned factor. Southern blot and nucleo tide sequence analyses revealed a related gene in Drosophila melanogas ter (the lola gene) previously identified by a genetic approach as inv olved in axon growth and guidance, Transfection assays in cells in cul ture with lola gene expression vectors and in situ hybridization exper iments with lola gene mutants finally provided evidence that the copia retrotransposon is regulated by this neurogenic gene in D. melanogast er, with a repressor effect in the central nervous systems of the embr yos.