The Bloom’s Syndrome Gene Product Is a 3′-5′ DNA Helicase*
- From the Imperial Cancer Research Fund Laboratories, Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DS, United Kingdom
Abstract
Bloom’s syndrome (BS) is an autosomal recessive condition characterized by short stature, immunodeficiency, and a greatly elevated frequency of many types of cancer. The gene mutated in BS, BLM, encodes a protein containing seven “signature” motifs conserved in a wide range of DNA and RNA helicases. BLM is most closely related to the subfamily of DEXH box-containing DNA helicases of which the prototypical member is Escherichia coli RecQ. To analyze its biochemical properties, we have overexpressed an oligohistidine-tagged version of the BLMgene product in Saccharomyces cerevisiae and purified the protein to apparent homogeneity using nickel chelate affinity chromatography. The recombinant BLM protein possesses an ATPase activity that is strongly stimulated by either single- or double-stranded DNA. Moreover, BLM exhibits ATP- and Mg2+-dependent DNA helicase activity that displays 3′-5′ directionality. Because many of the mutations in BS individuals are predicted to truncate the BLM protein and thus eliminate the “helicase” motifs or map to conserved positions within these motifs, our data strongly suggest that these mutations will disable the 3′-5′ helicase function of the BLM protein.
Footnotes
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↵* This work was supported in part by the Imperial Cancer Research Fund.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ Supported by Boehringer Ingelheim Fonds.
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↵§ Medical Research Council Clinical Training Fellow.
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↵¶ To whom correspondence should be addressed. Tel.: 44-1865-222417; Fax: 44-1865-222431; E-mail:hickson{at}icrf.icnet.uk.
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↵1 The abbreviations used are: BS, Bloom’s syndrome; kb, kilobase pair(s); ORF, open reading frame; rBLM, recominant BLM; PAGE, polyacrylamide gel electrophoresis; bp, base pair.
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- Received September 30, 1997.
