New Technology Unveils DNA Replication's Hidden Secrets

Spanish researchers have developed a detailed atlas that characterizes the proteins comprising the replisome, the complex molecular machine that performs DNA replication.

The replisome must first unwind double stranded DNA into two single strands. For each of the resulting single strands, a new complementary sequence of DNA is synthesized. The net result is formation of two new double stranded DNA sequences that are exact copies of the original double stranded DNA sequence.

Some replisome proteins were already known, but the current study utilized a new technology that allowed identification of more proteins needed for DNA replication, opening up new research paths in the field. Investigators at the Spanish National Cancer Research Center (Madrid) developed an approach that combined the isolation of proteins on nascent DNA chains with mass spectrometry (iPOND-MS), allowing a comprehensive proteomic characterization of the human replisome and replisome-associated factors. The iPOND method (procedure to isolate proteins on nascent DNA) can be applied to any proliferating cell type. It relies on the incorporation of a chemical label into newly synthesized DNA. The label can be modified by a chemistry reaction, and proteins linked to the DNA can be isolated and characterized. The Spanish investigators combined iPOND with sensitive mass spectroscopy (MS) analysis.

They reported in the March 28, 2013, issue of the journal Cell Reports that in addition to known replisome components, they had compiled a broad list of proteins that resided in the vicinity of the replisome, some of which were not previously associated with replication. For instance, their data supported a link between DNA replication and the Williams-Beuren syndrome, an autosomal gene deletion disorder involving over 17 genes on chromosome 7 that is characterized by a broad spectrum of abnormalities, and identified the protein ZNF24 (zinc finger protein 24) as a replication factor.

"We suspected that there might be several dozen proteins that control this process meticulously, thus ensuring the correct duplication of our genome as an indispensable step prior to cell division," said senior author Dr. Óscar Fernández-Capetillo, head of the genomic instability group at the Spanish National Cancer Research Centre. "The proteins identified have very different activities: they open up the DNA double helix, copy it, repair any breaks if needs be, modify it in different ways, etc. In short, they are all necessary in order to ensure the correct duplication of the DNA and avoid aberrations in the genetic material that form the basis of tumors. If we manage to find fundamental differences between replication in normal cells and in cancer cells, we will surely be able to find new therapeutic targets on which to focus future treatments in the fight against cancer."

Related Links:
Spanish National Cancer Research Center