The process by which genes are duplicated is mysterious and complex, involving a cast of characters with diverse talents and the ability to play well with others in extremely close quarters. A key player on this stage is an enzyme called a helicase. Its job is to unwind the tightly coiled chain of nucleic acids the DNA or RNA molecule that spells out the organisms genetic code so that another enzyme, a polymerase, can faithfully copy each nucleotide in the code.
Researchers at the University of Illinois, Yale University and the Howard Hughes Medical Institute have shed new light on how the Hepatitis C helicase plays this role, using a technique developed at Illinois that can track how a single molecule of RNA or DNA unwinds. Their research findings appear tomorrow in the journal, Science.
Getting at the underlying mechanisms of replication is no easy task. Structural studies involve crystallizing the DNA-protein complexes to see how they interact. Biochemists look at the agents of a reaction, the energy used and how much time lapses between steps. Such studies measure the behavior of hundreds of thousands of molecules at a time, and the results describe a whole population of reactions.
Using single-molecule fluorescence analysis, the research team tracked how the hepatitis C helicase, NS3, unwound a duplexed DNA molecule tagged with a fluorescent label on each strand of its double-stranded region. (The NS3 helicase is primarily involved in unwinding the single-stranded RNA of the hepatitis virus, but it can also act on DNA. This suggests that the helicase plays a role in unwinding double-stranded host DNA during infection. The duplex created for the experiment included both single- and double-stranded DNA; fluorescent labels were located in the double-stranded region.)
By tracking the gradually increasing distance between the two marked nucleotides as the strands separated in an unwinding event, the researchers were able
Contact: Diana Yates
University of Illinois at Urbana-Champaign