Localization of chi1-related helicase genes to human chromosome regions 12p11 and 12p13: similarity between parts of these genes and conserved human telomeric-associated DNA.

The helicase enzymes are essential components of a number of multi-protein complexes, including those that regulate transcription, splicing, translation, and DNA repair. These enzymes assist in the unwinding of double-stranded DNA and RNA as an essential part of their function. The yeast Chl1 gene encodes a putative helicase that appears to be essential for normal chromosome transmission. Human cDNAs related to this yeast gene, hCHLR1 and hCHLR2, were recently isolated and shown to encode products that localize to the nucleus. Two corresponding genes have now been partially characterized and localized to human chromosome regions 12p11 and 12p13, indicating that this gene is contained within a duplicated region localized to 12p. In addition, a comparison of the hCHLR gene sequences with available databases indicates that a large portion of these genes, including exons encoding two functional domains of the carboxyl-terminal region of these proteins, has been duplicated as part of a larger human telomeric repeat sequence found on many human chromosomes. Our results suggest that duplication of a relatively large region of chromosome 12p containing this putative helicase gene has resulted in the creation of numerous pseudogenes as part of a subtelomeric repeat. The presence of these helicase pseudogenes, as well as pseudogenes for other genes such as the interleukin-9 receptor, within many subtelomeric regions support the possibility that the spread of this region is subject to exchange between different chromosomes and may have implications for elucidation of the mechanism of intra- and interchromosomal duplication events.