Sturcture and expression of the humanXPBC/ERCC-3gene involved in DNA repair disorders xeroderma pigmentosum and Cockayne's syndrome

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Abstract
The human XPBC/ERCC-3 was cloned by virtue of its ability to correct the excision repair defect of UVsensitive rodent mutants of complementation group 3. The gene appeared to be in addition implicated in the human, cancer prone repair disorder xeroderma pigmentosum group B, which is also associated with Cockayne's syndrome. Here we present the genomic architecture of the gene and its expression. The XPBC/ERCC-3 gene consists of at least 14 exons spread over approximately 45 kb. Notably, the donor splice site of the third exon contains a GC instead of the canonical GT dinucleotide. The promoter region, first exon and intron comprise a CpG island with several putative GC boxes. The promoter was confined to a region of 260 bp upstream of the presumed cap site and acts bidirectionally. Like the promoter of another excision repair gene, ERCC-1, it lacks classical promoter elements such as CAAT and TATA boxes, but it shares with ERCC-1 a hitherto unknown 12 nucleotide sequence element, preceeding a polypyrimidine track. Despite the presence of (AU)-rich elements in the 3′-untranslated region, which are thought to be associated with short mRNA half-life actinomycin-D experiments indicate that the mRNA is very stable (t 1/2<3h). Southern blot analysis revealed the presence of XPBC/ERCC-3 cross-hybridizing fragments elsewhere in the genome, which may belong to a related gene.