The human repair gene ERCC6-a presumed DNA (or RNA) heilcase-has recently been found to function specifically in preferential nucieotide excision repair (NER). This NER subpathway is primarily directed towards repair of (the transcribed strand of) active genes. Mutations in the ERCC6 gene are responsible for the human hereditary repair disorder Cockayne's syndrome complementation group B, the most common form of the disease. in this report, the genomic organization and expression of this gene are described. It consists of at least 21 exons, together with the promoter covering a region of 82-90 kb on the genome. Postuiated functionai domains deduced from the predicted amino acid sequence, inciuding 7 distinct heiicase signatures, are-with one exception-encoded on separate exons. Consensus spilce donor and acceptor sequences are present at au exon borders with the exception of the unusual splice donor at the end of exon VII. The "invarlabie" GT dinucleotide in the consensus (C, A)AG/GTPuAGT is repiaced by the exceptional GC. Based on 42 GC spiice donor sequences identified by an extensive literature search we found a statisticaliy highly significant better "overall" match of the surrounding nucleotides to the consensus sequence compared to normal GT-sites. This confirms and extends the observation made recently by Jackson (Nucl. Acids Res., 19, 3795-3798 (1991)) derived from anaiysis of 26 cases. Anaiysis of ERCC6 cDNA clones revealed the occurrence of alternative polyadenylation, resulting in the (differential) expression of two mRNA molecules (which are barely detectable on Northern biots) of 5 and 7 kb in length.