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Homologous Recombination Essay

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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 …show more content…

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

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In which case, the nuclear envelope is visible again and the DNA uncoil into chromatin. No DNA replication occurs during interphase II. In prophase II, the nuclear envelope disintegrates again, and the chromosomes stay in sister chromatid form (if they unraveled into chromatin during interphase II they condense again). In metaphase II, spindle fibers from opposing poles of the cell attach to the centromeres of each sister chromatid. Sister chromatids are two identical copies/strands connected by one centromere that results from the replication of a chromosome during the S phase.

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The study also found that an increase in γ-H2AX (a marker for DNA double-strand breaks) and a decrease in RAD1 (a marker of HR directed DNA repair) focus-positive cells was associated with a depletion of MEN1 expression as predicted. The study also predicted that NHEJ could function to repair double strand breaks, and would increase with a loss of MEN1 functionality. The study found this prediction to be true. The study also investigated the role of ATM and ATR DNA damage kinases in relation to MEN1, and found that MEN1 is protected from ubiquitin mediated degradation through phosphorylation by ATM and ATR protein kinases. One of the most significant results from this study involved determining the functional relationship between the expression of HR target genes and MEN1, as well as investigating the mechanism of action involved in the cellular process.

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Furthermore, Acinetobactor baylyi ADP1 like most organisms undergoes a process known as DNA recombination, where two complementary DNA strands cross and exchange portions of DNA. During recombination, a structure known as a Holliday Junction forms and must be resolved, completing the exchange of DNA (Aravind et al. 2000). Recombination is a crucial mechanism in both gene amplification and deletion. Specifically, ADP1 contains a protein called YqgF, a putative Holliday Junction Resolvase, due to its structural similarity to a known resolvase named RuvC (Aravind et al.

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