Genomic structure and characterization of the Drosophila S3 ribosomal/DNA repair gene and mutant alleles

The Drosophila S3 protein is known to be associated with ribosomes, where i t is thought to play a role in the initiation of protein translation. The S 3 protein also contains a DNA repair activity, efficiently processing 8-oxo guanine residues in DNA via an N-glycosylase/apurinic-apyrimidinic (AP) lya se activity. The gene that encodes S3 has previously been localized to one of the Minute loci on chromosome 3 in Drosophila. This study focused on the genomic organization of S3 at M(3)95A, initial promoter characterization, and analysis of three mutant alleles at this locus. The S3 gene was found t o be a single-copy gene 2 to 3 kb in length and containing a single intron. The upstream 1,6-kb region was analyzed for promoter activity, identifying a presumptive regulatory domain containing potential enhancer and suppress or elements, This finding is of interest, as the S3 gene is constitutively expressed throughout development and mRNA is most likely maternally inherit ed. Lastly, three Minute alleles from the same locus were sequenced and two alleles found to contain a 22-bp deletion in exon 2, resulting in a trunca ted S3 protein, although wildtype levels of S3 mRNA and protein were detect ed in the viable heterozygous Minute alleles, possibly reflecting dosage co mpensation.