Homologous Recombination Essay

Homologous recombination (HR) can be explained as a process where DNA is exchanged or copied between two chromosomes or different regions of the same chromosome. The process requires homology between the exchanging DNA regions. Homologous recombination repairs DNA breaks, especially double stranded breaks (DSBs), stabilizes and repairs stalled forks. HR consists of a series of inter related pathways that function in repair of DNA breaks (Figure 4). Initially, stretches of single stranded DNA (ssDNA) are resected at the stalled forks or DSB ends which are quickly bound by replication protein A (RPA). Rad51 replaces RPA and binds to these ssDNA with the aid of the Rad52 mediator function (21,22). Rad51 form a nucleoprotein filament, which can then engage in homology search by strand invasion forming a homologous DNA

Yet another category of translocations is Robertsonian translocations, which are formed due to rearrangements of centromere repeat sequences of two acrocentric chromosomes, forming a single large chromosome (Figure 5). Robertsonian translocation that cause several genetic diseases in humans such as Patau syndrome, Down’s syndrome (39). On the other hand, translocation on the same chromatid gives rise to arms that are mirror images of each other known as isochromosomes. Isochromosomes are frequently observed in specific types of cancer (40) and those of chromosome X can cause Turner syndrome (41). In S. pombe, translocations and isochromosomes were formed by the rearrangement of centromere repeats that were suppressed by HR factor Rad51 (31). Rad51 and Rad54 promote non-crossover recombination between centromere inverted repeats thereby suppressing crossover recombination resulting in inversion and isochromosome formation (30,31). Therefore, HR is crucial for suppressing rearrangements in centromere