RAD51

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RAD51 is a eukaryotic protein with a crucial role in DNA repair, specifically in homologous recombination (HR). Here's a breakdown of what RAD51 is and its functions:
What is RAD51?

• Homolog of RecA: RAD51 is a protein encoded by the *RAD51* gene. It is homologous to the bacterial RecA protein, Archaeal RadA, and yeast Rad51, meaning they share a common evolutionary ancestor and have similar functions.
• DNA Repair: RAD51 is essential for repairing damaged DNA, particularly double-strand breaks (DSBs). These breaks can be caused by things like radiation, environmental exposures, or during normal cellular processes like DNA replication.
• Protein Family: It's a member of the RAD51 protein family, all of which assist in repairing DNA double-strand breaks.
• Conserved Protein: The RAD51 protein structure is highly conserved across many eukaryotes, from yeast to humans.

• Homologous Recombination: RAD51 plays a major role in homologous recombination (HR), a process that uses an undamaged homologous DNA sequence as a template to repair a broken DNA strand.
• Strand Exchange: During HR, RAD51 catalyzes a DNA strand exchange. A template strand invades base-paired strands of homologous DNA molecules.
• Nucleoprotein Filament: RAD51 forms a helical nucleoprotein filament on single-stranded DNA (ssDNA). This filament is crucial for the strand-pairing reactions in DNA recombination.
• Homology Search: RAD51 is involved in searching for the homologous DNA sequence and pairing the strands.
• Interaction with Other Proteins: To perform its functions, RAD51 interacts with several other proteins, including:
• RPA: ssDNA-binding protein.
• BRCA1 and BRCA2: These proteins are also involved in DNA repair, and their interaction with RAD51 is vital. BRCA2 helps regulate RAD51 by transporting it to the damage sites.
• RAD52, RAD54L, RAD54B, XRCC3: Other proteins involved in homologous recombination.
• PALB2: Serves as a scaffold for a HR complex.
• RAD51AP1 and RAD51AP2.
• Replication Stress: Besides double-strand break repair, RAD51 also helps overcome replication stress, such as when DNA replication forks stall. It's involved in fork reversal, protecting reversed forks, repairing, restarting broken replication forks, and post-replicative gap filling.

• RAD51, together with another recombinase called Dmc1, has a vital role during meiosis (cell division that produces sex cells). Both proteins form filaments on single-stranded DNA that promote recombination between homologous chromosomes.

• RAD51 is frequently over-expressed in various cancers. In many studies, elevated RAD51 is linked to decreased patient survival, indicating a role of RAD51 in resisting radio or chemotherapies.
• However, there are conflicting reports on the effects, with under-expression of RAD51 is also reported in some other cancers.