The C-terminal domain of the Bloom syndrome DNA helicase is essential for genomic stability.
BACKGROUND
Bloom syndrome is a rare cancer-prone disorder in which the cells of affected persons have a high frequency of somatic mutation and genomic instability. Bloom syndrome cells have a distinctive high frequency of sister chromatid exchange and quadriradial formation. BLM, the protein altered in BS, is a member of the RecQ DNA helicase family, whose members share an average of 40% identity in the helicase domain and have divergent N-terminal and C-terminal flanking regions of variable lengths. The BLM DNA helicase has been shown to localize to the ND10 (nuclear domain 10) or PML (promyelocytic leukemia) nuclear bodies, where it associates with TOPIIIalpha, and to the nucleolus.


RESULTS
This report demonstrates that the N-terminal domain of BLM is responsible for localization of the protein to the nuclear bodies, while the C-terminal domain directs the protein to the nucleolus. Deletions of the N-terminal domain of BLM have little effect on sister chromatid exchange frequency and chromosome stability as compared to helicase and C-terminal mutations which can increase SCE frequency and chromosome abnormalities.


CONCLUSIONS
The helicase activity and the C-terminal domain of BLM are critical for maintaining genomic stability as measured by the sister chromatid exchange assay. The localization of BLM into the nucleolus by the C-terminal domain appears to be more important to genomic stability than localization in the nuclear bodies.
Yankiwski
V
V
Laboratory of Molecular Genetics, New York Blood Center, 310 East 67th Street, New York, NY 10021, USA. nneff@nybc.org
Noonan
J P
JP
Neff
N F
NF
D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D000483:Alleles; D002461:Cell Line, Transformed; D002466:Cell Nucleolus / Q000201:enzymology; D002467:Cell Nucleus / Q000201:enzymology; D002875:Chromosomes / Q000648:ultrastructure; D004265:DNA Helicases / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D004260:DNA Repair; D004305:Dose-Response Relationship, Drug; D004318:Doxycycline / Q000494:pharmacology; D016678:Genome; D049452:Green Fluorescent Proteins; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics; D009154:Mutation; D017434:Protein Structure, Tertiary; D053484:RecQ Helicases; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012854:Sister Chromatid Exchange; D015533:Transcriptional Activation; D014162:Transfection
D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D000251:Adenosine Triphosphatases; C097151:Bloom syndrome protein; D004265:DNA Helicases; D053484:RecQ Helicases; D004318:Doxycycline