Abstract
BLM, the helicase mutated in Bloom syndrome, associates with topoisomerase 3alpha, RMI1 (RecQ-mediated genome instability), and RPA, to form a complex essential for the maintenance of genome stability. Here we report a novel component of the BLM complex, RMI2, which interacts with RMI1 through two oligonucleotide-binding (OB)-fold domains similar to those in RPA. The resulting complex, named RMI, differs from RPA in that it lacks obvious DNA-binding activity. Nevertheless, RMI stimulates the dissolution of a homologous recombination intermediate in vitro and is essential for the stability, localization, and function of the BLM complex in vivo. Notably, inactivation of RMI2 in chicken DT40 cells results in an increased level of sister chromatid exchange (SCE)--the hallmark feature of Bloom syndrome cells. Epistasis analysis revealed that RMI2 and BLM suppress SCE within the same pathway. A point mutation in the OB domain of RMI2 disrupts the association between BLM and the rest of the complex, and abrogates the ability of RMI2 to suppress elevated SCE. Our data suggest that multi-OB-fold complexes mediate two modes of BLM action: via RPA-mediated protein-DNA interaction, and via RMI-mediated protein-protein interactions.
Publication types
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Research Support, N.I.H., Intramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Amino Acid Sequence
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Animals
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Bloom Syndrome / metabolism*
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Carrier Proteins / genetics
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Carrier Proteins / metabolism*
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Cell Nucleus / metabolism
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Cells, Cultured
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Chickens
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DNA Damage
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DNA Helicases / physiology*
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DNA Repair
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DNA Topoisomerases, Type I / physiology
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DNA, Cruciform
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DNA, Single-Stranded / genetics
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DNA, Single-Stranded / metabolism
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism*
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Genomic Instability*
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HeLa Cells
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Humans
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Mitosis
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Molecular Sequence Data
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Nuclear Proteins / genetics
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Nuclear Proteins / metabolism*
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Oligonucleotides / chemistry
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Oligonucleotides / genetics
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Oligonucleotides / metabolism
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Phosphorylation
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Protein Folding
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RecQ Helicases
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Recombinant Proteins / genetics
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Recombinant Proteins / isolation & purification
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Recombinant Proteins / metabolism
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Recombination, Genetic
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Replication Protein A / genetics
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Replication Protein A / metabolism*
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Sequence Homology, Amino Acid
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Sister Chromatid Exchange
Substances
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Carrier Proteins
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DNA, Cruciform
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DNA, Single-Stranded
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DNA-Binding Proteins
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Nuclear Proteins
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Oligonucleotides
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RMI1 protein, human
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RMI2 protein, human
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RPA1 protein, human
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Recombinant Proteins
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Replication Protein A
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Bloom syndrome protein
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DNA Helicases
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RecQ Helicases
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DNA Topoisomerases, Type I