“This is the first time anyone has shown that nanopores can be used to generate interpretable signatures corresponding to very long DNA sequences from real-world genomes,” said co-author Jay Shendure, a UW associate professor of genome sciences whose lab develops applications of genome sequencing technologies. “It’s a major step forward.”
UW researcher used the nanopore Mycobacterium smegmatis porin A (MspA). This bacterial pore has been genetically altered so that the narrowest part of the channel has a diameter of about a nanometer, or 1 billionth of a meter. This is large enough for a single strand of DNA to pass through. The modified nanopore is then inserted into a membrane separating two salt solutions to create a channel connecting the two solutions.
To read a sequence of DNA with this system, a small voltage is applied across the membrane to make the ions of the salt solution flow through the nanopore. The ion flow creates a measurable current. If a strand of DNA is added to the solution on one side of the membrane and then enters a pore, the bulky DNA molecules will impede the flow of the much smaller ion and thereby alter the current. How much the current changes depends on which nucleotides -- the individual molecules adenine, guanine, cytosine and thymine that make up the DNA chain -- are inside the pore. Detecting changes in current can reveal which nucleotides are passing through the nanopore’s channel at any given instant.