BRCA2, Breast Cancer 2 susceptibility protein, is encoded by BRCA2 gene mapped to 13q12.3. BRCA2 repairs DNA damage through homologous recombinbation, the exchange of identical or nearly identical sequences of DNA. Homologous recombination occurs mostly during sexual reproduction or repair of DNA damage. Unrepaired, DNA damage leads to mutations in the cell line, and eventually, cancer. Without BRCA2 protein, our body's ability to repair DNA damage and avoid cancer are seriously hindered. That is why people with defective BRCA2 are susceptible to breast cancer. DNA damage goes unrepaired, and cells behave aberrantly.
Now, what's fascinating about BRCA2 is that we originally discovered its function by looking at its homolog in the fungi Ustilago maydis, the corn smut. Scientists sequenced the peptide chain the known damage repair protein in U. maydis and compared it with proteins of unknown function in humans. Proteins in humans that have the same function will have similar sequences, because amino acid sequence determines protein structure, affinity, and function. Amazing, isn't it?
People often ask me why I chose microbiology. Microbes are great organisms to study genetically because of their small and haploid genomes, short generation cycle, and their ability to uptake free DNA through transformation. Small genomes are easier to map. Being haploid organisms, they only have one set of DNA, so changes in the DNA will have corresponding changes in their phenotype. Being haploid, they're asexual, so bacteria and other prokaryotes (including some unicellular eukaryotes) produce genetic clones in subsequent generations. Microbes' ability to uptake free DNA helped geneticists to easily manipulate their genomes before the advent of gene targeting in mammals.
It was only after Dr. Mario Capecchi's research we use homologous recombination to edit specific genes in mammals and actually play around with higher animal's genetics.
Article by UCD on the function of homologous recombination proteins in different model organisms:
Every time they mention HR they mean homologous recombination.
Interested in gene targeting in mice? Find out more!
Video of Dr. Mario Capecchi, 2007 Nobel Laureate:
Steps for homologous recbomination in mice: