THE DNA amplification technique that underpins much of modern biology and medicine has been made even easier to perform by eliminating the need to heat samples to near boiling point. The breakthrough might lead to the development of cheaper, more portable equipment for purposes such as diagnosing diseases.
The polymerase chain reaction (PCR) is the basis of myriads of genetic tests 鈥� from detecting viruses such as HIV in blood and spotting disease-causing mutations in our genes to obtaining DNA fingerprints from crime scenes or extracting ancient DNA from fossils. These tests depend on PCR to generate millions of copies of a sequence of target DNA, even if a sample contains just one copy of this sequence to begin with.
Numerous variations on PCR have been developed but all rely on at least one heating step to make double-stranded DNA uncoil and separate into single strands. Standard PCR involves many cycles of heating and cooling (see Graphic), which means the equipment is relatively bulky and power-hungry.
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But now New England Biolabs, a company based in Beverly, Massachusetts, has got the entire process working at a single temperature, thanks to one of a class of proteins called helicases that uncoil double-stranded DNA in cells. The team also adds 鈥渟ingle-strand binding proteins鈥� to the sample, which may help keep the two strands apart after the helicase has separated them.
The new method is called helicase-dependent amplification, or HDA. Given that the uncoiling function of helicases has been known since the 1970s, team leader Huimin Kong says he was amazed to discover, when his company applied for a patent 18 months ago, that no other teams appear to have tried using helicases as a replacement for heating in PCR.
The Biolabs team has already done a string of successful experiments using the HDA technique, such as amplifying bacterial DNA in a blood sample (EMBO reports, DOI: 10.1038/sj.embor.7400200). 鈥淚t worked like a dream,鈥� says Kong.
Other experts say the technique is promising, but that HDA鈥檚 usefulness will depend on overcoming its limitations. At present, it is relatively slow, it can amplify only short sequences of DNA (up to about 200 base pairs long) and the reaction takes place at 37 掳C, which means some heating is still required.
Kong is confident of solving these problems, though. With hundreds of natural helicases to choose from, for instance, he thinks it should be possible to get the reaction working at room temperature.