Tokyo Metropolitan University researchers have been investigating homologous recombination, a process in which double-stranded DNA breaks are repaired by the RecA protein by reassembling a broken strand into an intact double strand and patching the break according to the intact sequence. Researchers found that RecA knows just where to insert the single strand into the double helix without ever twisting it. Their discoveries offer fresh approaches to the study of cancer.
A pervasive biochemical process that all living organisms, including plants, animals, fungi, and bacteria, engage in is called homologous recombination (HR). Our DNA is exposed to a variety of external and internal stresses throughout our daily lives, some of which have the potential to split the double helix’s two strands. This can be extremely harmful and result in impending cell death. Fortunately, procedures like HR are always undoing this harm.
RecA Protein Omits The DNA Repair Process
Resection occurs when one of the two exposed ends of the helix break separates during HR, exposing an exposed single-stranded end. Next, a neighbouring intact double strand and the exposed single strand are bound by a protein called RecA Protein (or a protein similar to it). The protein then “searches” for the identical sequence. Strand invasion is the method by which it recombines the single strand into the double helix at the appropriate location.
Then, using the preexisting DNA as a template, the broken DNA strand is repaired. HR is essential to biodiversity because it permits precise double-strand break repair and genetic information exchange. However, the precise molecular picture of HR remains unclear, particularly the consequences of RecA protein carrying both the single and double strands.
RecA protein
Researchers at Tokyo Metropolitan University under the direction of Professor Kouji Hirota have been examining DNA repair mechanisms such as HR. They attempted to test two opposing theories regarding what transpires when HR arises in their most recent experiment. RecA does a “homology search,” wherein it unwinds a portion of the double strand in an attempt to locate the ideal location for strand invasion. In the second, unwinding does not happen following RecA binding; rather, unwinding only happens upon strand invasion.
The group used two strategies in collaboration with a group from the Tokyo Metropolitan Institute of Medical Science to address which of these truly occurs. In the first, they investigated if this had an impact on DNA repair by using a mutant of RecA protein that is unable to unwind the strand or separate the double strands. As it happens, this has very little impact. In the second, they attempted to quantify the amount of torsion generated in the strand at various points during the procedure.
They discovered that the only unwinding-related torsion they could find happened when strand invasion took place, that is, after the homology search was finished. The researchers demonstrated for the first time that the second model was accurate.
In-depth knowledge of homologous recombination is essential to comprehending the consequences of errors. For instance, BRCA1 and BRCA2, which are linked to breast cancer, are also in charge of ensuring that single-stranded DNA is correctly loaded onto RAD51, the human form of RecA. This implies that people with inherited abnormalities in BRCA1 or BRCA2 may have a higher prevalence of breast cancer due to HR issues. The group anticipates that results such as theirs will open up new avenues for cancer research.
