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Technology: Dyes could speed up the genome project . . .

作者:权鸦挠    发布时间:2019-03-02 02:01:06    

By ANDY COGHLAN The human genome project to decipher the entire genetic ‘blueprint’ of human beings could take decades to complete at its current rate, but two researchers in the US are developing a technique that they say could do the job 4000 times as fast. Robert Levis and Louis Romano, of the chemistry department of Wayne State University in Detroit, have devised a way to read genetic code using mass spectrometry, a common analytical tool used to find the constituents of chemical compounds. The problem with using such a machine on DNA is that before it can be analysed, the DNA must be vaporised and ionised, a process which has proved difficult in the past. The researchers have found a way to prepare the DNA samples using dyes. Their short cut should enable analysts to examine fragments of DNA in seconds. Normally, it would take skilled analysts hours to probe the same fragments. The genetic information in DNA is constructed from just four chemical subunits or bases. The order of these four bases along the strands of DNA defines the genetic code. But mapping this code using the conventional process of electrophoresis is painfully slow. Electrophoresis involves splitting up a sample of DNA with enzymes, ionising the fragments and applying them in blobs to a gel which is spread over a glass slide. The analysts ‘pull’ the fragments up the slide in a smear using an electric field. The lighter fragments are easier to ‘pull’ and so reach higher points on the gel. From these positions, the analysts can work out the weight of the DNA fragment and so the sequence of bases. The whole process can take 15 hours, says Romano. In the new technique under investigation at Wayne University, Levis and Romano immerse the DNA fragments in a red dye – called Rhodamine 6G – which absorbs green light. They vaporise the sample by shining a specific wavelength of green light onto it in a burst lasting five billionths of a second. This vaporises the dye and DNA fragments with it but does not disintegrate the DNA any further. The fragments also need to be ionised. The researchers achieve this by tagging a second dye to the DNA sample before it is vaporised. This second dye is designed to attach to all the fragments. Once the fragments are vaporised, the researchers shine a laser on the dye-laden fragments at a specific wavelength. The dye molecules lose an electron, leaving them charged. The fragments, with the charged dye attached, are then ready for the mass spectrometer. This accelerates them to a specific speed using an electric field and then bends their paths into a curve with a magnetic field. Heavier fragments, with more momentum, will be bent less by the magnetic field so the amount of bending tells the spectrometer the mass of the fragment. The analysis takes seconds. Romano says so far, he and colleagues have managed to vaporise and ionise strands of DNA 1000 bases long – more than three times as long as those commonly analysed using electrophoresis. They have only tested much shorter strands – about five bases long – in a mass spectrometer, so there is some way to go before the technique is practical. ‘But (an instrument) could be up and running by the end of the year,

 

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