Bloom syndrome protein

Bloom syndrome protein is a is_associated_with::protein that in humans is encoded by the BLM is_associated_with::gene and is not expressed in is_associated_with::Bloom syndrome.

The Bloom syndrome gene product is related to the is_associated_with::RecQ subset of DExH box-containing DNA is_associated_with::helicases and has both DNA-stimulated is_associated_with::ATPase and ATP-dependent DNA helicase activities. Mutations causing is_associated_with::Bloom syndrome delete or alter helicase motifs and may disable the 3' → 5' helicase activity. The normal protein may act to suppress inappropriate is_associated_with::homologous recombination.

is_associated_with::Meiosis
Recombination during is_associated_with::meiosis is often initiated by a DNA double-strand break (DSB). During recombination, sections of DNA at the 5' ends of the break are cut away in a process called resection. In the strand invasion step that follows, an overhanging 3' end of the broken DNA molecule then "invades" the DNA of an homologous chromosome that is not broken. After strand invasion, the further sequence of events may follow either of two main pathways leading to a crossover (CO) or a non-crossover (NCO) recombinant (see is_associated_with::Genetic recombination and bottom of Figure in this section).

The budding yeast is_associated_with::Saccharomyces cerevisiae encodes an ortholog of the Bloom syndrome (BLM) protein that is designated is_associated_with::Sgs1 (Small growth suppressor 1). Sgs1(BLM) is a is_associated_with::helicase that functions in is_associated_with::homologous recombinational repair of DSBs. The is_associated_with::Sgs1(BLM) helicase appears to be a central regulator of most of the recombination events that occur during S. cerevisiae is_associated_with::meiosis. During normal meiosis Sgs1(BLM) is responsible for directing recombination towards the alternate formation of either early NCOs or is_associated_with::Holliday junction joint molecules, the latter being subsequently resolved as COs.

In the plant is_associated_with::Arabidopsis thaliana, homologs of the Sgs1(BLM) helicase act as major barriers to meiotic CO formation. These helicases are thought to displace the invading strand allowing its annealing with the other 3’overhang end of the DSB, leading to NCO recombinant formation by a process called synthesis dependent strand annealing (SDSA) (see is_associated_with::Genetic recombination and Figure in this section). It is estimated that only about 5% of DSBs are repaired by CO recombination. Sequela-Arnaud et al. suggested that CO numbers are restricted because of the long-term costs of CO recombination, that is, the breaking up of favorable genetic combinations of alleles built up by past is_associated_with::natural selection.

Interactions
Bloom syndrome protein has been shown to interact with:


 * ATM,
 * is_associated_with::CHAF1A,
 * is_associated_with::CHEK1,
 * is_associated_with::FANCM,
 * FEN1,
 * is_associated_with::H2AFX,
 * is_associated_with::MLH1
 * is_associated_with::P53,
 * is_associated_with::RAD51L3,
 * is_associated_with::RAD51,
 * RPA1,
 * is_associated_with::TOP3A,
 * is_associated_with::TP53BP1,
 * WRN, and
 * is_associated_with::XRCC2.