**3.4 Post-synaptic phase of HR – Resolution of Holliday junction**

Following the synaptic phase, D-loops can be eliminated by different subpathways, each requiring different proteins. Here we will present only the pathways involving double Holliday junctions (dHJ) (Bzymek et al., 2010). Double HJ are structural intermediates which are resolved by specific endonucleases and result in either crossover or non-crossover products. The dHJ intermediates can also be resolved by helicases (RecQ helicase family) combined with topoisomerase action. In human cells, this pathway combines BLM helicase and topoisomerase IIIa, both of which catalyze dHJ dissolution (Wu and Hickson, 2003). Interestingly, BLM helicase is phosphorylated by different kinases, such as Chk1, at different stages of the cell cycle or in response to DNA damage. BLM can interact with 53PB1, a signal transducer, and with Topoisomerase IIIa during the presynaptic and the postsynaptic phases of HR respectively. It has been shown that BLM and 53BP1 can interact physically with Rad51 and regulate HR by modulating the assembly of Rad51 filaments. The *in vivo* phosphorylation of both BLM and 53BP1 affects negatively Rad51 foci formation (Tripathi et al., 2007). Concerning Topoisomerase IIIa, Rao and colleagues suggested that the BLM phosphorylation on T99 results in its dissociation from topoisomerase IIIa, thereby modulating the resolution of dHJ (Rao et al., 2005).

Posttranslational Modifications of Rad51 Protein and Its Direct Partners:

**6. References** 

280.

1247-1254.

32931-32935.

12752.

1756s.

6633-6643.

19516.

Cell *12*, 1087-1099.

Cell *39*, 333-345.

Mol Biol *339*, 797-804.

DNA repair protein. Mol Cell *7*, 273-282.

Role and Effect on Homologous Recombination – Mediated DNA Repair 155

Benore-Parsons, M., Seidah, N.G., & Wennogle, L.P. (1989). Substrate phosphorylation

Binz, S.K., Sheehan, A.M., & Wold, M.S. (2004). Replication protein A phosphorylation and the cellular response to DNA damage. DNA Repair (Amst) *3*, 1015-1024. Buisson, R., Dion-Cote, A.M., Coulombe, Y., Launay, H., Cai, H., Stasiak, A.Z., Stasiak, A.,

Bzymek, M., Thayer, N.H., Oh, S.D., Kleckner, N., & Hunter, N. (2010). Double Holliday junctions are intermediates of DNA break repair. Nature *464*, 937-941. Chen, C.F., Chen, P.L., Zhong, Q., Sharp, Z.D., & Lee, W.H. (1999a). Expression of BRC

Chen, G., Yuan, S.S., Liu, W., Xu, Y., Trujillo, K., Song, B., Cong, F., Goff, S.P., Wu,

Chen, J.J., Silver, D., Cantor, S., Livingston, D.M., & Scully, R. (1999c). BRCA1, BRCA2, &

Conilleau, S., Takizawa, Y., Tachiwana, H., Fleury, F., Kurumizaka, H., & Takahashi, M.

Davies, A.A., Masson, J.Y., McIlwraith, M.J., Stasiak, A.Z., Stasiak, A., Venkitaraman, A.R.,

Deng, X., Prakash, A., Dhar, K., Baia, G.S., Kolar, C., Oakley, G.G., & Borgstahl, G.E. (2009).

Dong, Y., Hakimi, M.A., Chen, X., Kumaraswamy, E., Cooch, N.S., Godwin, A.K., &

Dong, Z., Zhong, Q., & Chen, P.L. (1999). The Nijmegen breakage syndrome protein is

Dou, H., Huang, C., Singh, M., Carpenter, P.B., & Yeh, E.T. (2010). Regulation of DNA repair

can inhibit proteolysis by trypsin-like enzymes. Arch Biochem Biophys *272*, 274-

Xia, B., & Masson, J.Y. (2010). Cooperation of breast cancer proteins PALB2 and piccolo BRCA2 in stimulating homologous recombination. Nat Struct Mol Biol *17*,

repeats in breast cancer cells disrupts the BRCA2-Rad51 complex and leads to radiation hypersensitivity and loss of G(2)/M checkpoint control. J Biol Chem *274*,

Y., Arlinghaus, R.*, et al.* (1999b). Radiation-induced assembly of Rad51 and Rad52 recombination complex requires ATM and c-Abl. J Biol Chem *274*, 12748-

Rad51 operate in a common DNA damage response pathway. Cancer Res *59*, 1752s-

(2004). Location of tyrosine 315, a target for phosphorylation by cAbl tyrosine kinase, at the edge of the subunit-subunit interface of the human Rad51 filament. J

& West, S.C. (2001). Role of BRCA2 in control of the RAD51 recombination and

Human replication protein A-Rad52-single-stranded DNA complex: stoichiometry and evidence for strand transfer regulation by phosphorylation. Biochemistry *48*,

Shiekhattar, R. (2003). Regulation of BRCC, a holoenzyme complex containing BRCA1 and BRCA2, by a signalosome-like subunit and its role in DNA repair. Mol

essential for Mre11 phosphorylation upon DNA damage. J Biol Chem *274*, 19513-

through deSUMOylation and SUMOylation of replication protein A complex. Mol

Fig. 4. Schematic representation of Rad51 interactions with its direct partners involved in its posttranslational modification and the steps of HR (top). Localization of binding sites in the hRad51 sequence (bottom).
