Molecular characterization of the genomic regions of the Drosophilaα‐type submit proteasome genes PROS‐Dm28.1 and PROS‐Dm35

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Abstract
The proteasome (multicatalytic proteinase) consists of a large number of non‐identical protein subunits which are encoded by the evolutionarily conserved PROS gene family. Using the PROS‐Dm35 and PROS‐Dm28.1 cDNAs as probes, we have isolated the corresponding genomic DNA clones of Drosophila melanogaster. In situ hybridization shows that the members of the PROS gene family are not organized in a single gene cluster and that, in contrast to the PROS‐Dm35 gene, the PROS‐Dm28.1 gene is localized on the X chromosome. Analysis of the genomic organization of the PROS‐Dm28.1 and PROS‐Dm35 genes reveals that both genes are interrupted by two small introns whereby the relative positions of the introns within the two coding regions are not conserved. Neither gene possesses a distinct transcriptional start site as shown by nuclease S1 analysis. Since the promoter regions also do not contain a TATA box, PROS genes appear to be typical house‐keeping genes. A putative heat‐shock element in the promoter region of the PROS‐Dm35 gene was shown to be inactive on stress induction when fused to a reporter gene and tested in transient transfections assays. In addition, promoter deletion analysis demonstrates that the promoter region between positions –605 and –330 contains sequence elements important for PROS‐Dm35 gene activity and that deletions beyond position –150 result in an almost complete inhibition of transcription.