GENOMIC ORGANIZATION OF DHR38 GENE IN DROSOPHILA - PRESENCE OF ALU-LIKE REPEAT IN A TRANSLATED EXON AND EXPRESSION DURING EMBRYONIC-DEVELOPMENT

The recombinant lambda clone 4-2 containing the genomic region of the Drosophila hormone receptor 38 (DHR 38) gene, homologous to mammalian neuronal growth factor I-B (NGFI-B), was isolated by radioactive label led oligonucleotide hybridization. The nucleotide sequence of the geno mic clone revealed three exons that encode the functional domains of t he protein. The N-terminal exon1 had no homology at the amino acid lev el with NGFI-B, the mammalian homologue. A glutamine-rich region, prob ably involved in transcriptional activation, was observed at the C-ter minal part of this exon. A similar motif is also present upstream in a nother reading frame of the same strand. Both motifs are preceded by a repetitive nonanucleotide sequence containing an AluI site, resemblin g a duplicated human Alu-sequence. A monomeric version of this sequenc e, coding similarly for an oligoglutamine peptide, occurs at a surpris ingly high frequency in other regulatory genes in Drosophila. In contr ast to mammalian Alu sequences, this sequence is found almost exclusiv ely in the coding regions of Drosophila genes, but not in the non-codi ng parts of the genes.The DNA-binding domain with two zinc-fingers, an d at least part of the ligand-binding peptide, is coded by the largest middle exon2 in DHR38 and exhibits up to 100% homology in short pepti de motifs to its mammalian counterpart, where these domains are split into exons 3, 4, 5, and 6. However, the length, information content, s top codon, and splice site are conserved in the last exons in both fly and rat. In situ hybridization to 0-24 h wholemount embryos showed st rong expression of DHR38 in neurogenic regions and in the intestinal t ract during embryogenesis, suggesting a spatial and temporal control o f transcription, partially analogous to the central nervous system-spe cific expression of NGFI-B in mammals. Arch. Insect Biochem. Physiol. 38:185-192, 1998. (C) 1998 Wiley-Liss, Inc.