**5. Action of** *BRCA1* **and** *BRCA2* **proteins in DNA double strand damage repair**

Although the action of the *BRCA1* and *BRCA2* gene products in cancer causation is not fully discovered [9], their function in maintaining the genomic stability is well understood. This involves the DNA double strand break repair [DSB] which is the most deleterious type of DNA damage as no healthy DNA strand left for the repair mechanism [10]. The DSB will be repaired by 2 mechanisms in the healthy eukaryotic cells -The Homologous directed repair [HDR] pathway, which is a highly accurate system and Non-Homologous end joining [NHEJ] pathway which is prone to errors. BRCA1 and BRCA2 proteins involve in the HDR mechanism following stimulated by the cellular DNA damage response. This function is facilitated by other cellular proteins including RAD51 [11, 12], Ataxia-Telangiectasia kinase [ATM-kinase].

The following flow chart shows the mechanism of DNA DSB repair and the steps involving the BRCA1/2 proteins (**Figure 2**).

Mutation of the *BRCA1/2* genes causing loss of the encoded protein functions causes abnormal checkpoint stimulation and genomic errors in DNA repair

**Figure 2.**

*Action of BRCA1/2 protein in DNA double strand break repair. Source - functions of* BRCA1 *and* BRCA2 *in the biological response to DNA damage [13].*

causing cancer development through uncontrolled cellular proliferation, impaired cell apoptosis in abnormal cells.
