<p><span style="font-size:26px"><strong>Introduction</strong></span></p>

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<p><span style="font-size:26px"><strong>Denaturing phase of HDA</strong></span></p>

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<p><span style="font-size:16px">As helicase can unwind the double stranded DNA enzymatically, it is called isothermal amplification. In this process the HDA more special enzyme to make it real. The key component of the reagent is Uvrd, MutL, SSB, and ATP. Uvrd is the one of the helicase which was discovered in E coli so that it is the main enzyme in this process. And for the processivity of Uvrd, the DNA repair enzyme MutL, which helps Uvrd to be recruited on the DNA, is necessary.&nbsp;MutL activates Uvrd performance by more than 10times. SSB is short of single strand binding DNA. It binds to the denatured strand of DNA to stabilize it so that SSB protein prevent the immediate annealing of two single stranded DNA after denaturing happened.&nbsp;Lastly, ATP is required to both Uvrd and MutL performance. As you can see below figure, absence of each of key component is critical for denaturation process.&nbsp;</span></p>

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<p><span style="font-size:26px"><strong>Benefits and limits</strong></span></p>

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<p>Schematic diagram of HDA. Two complementary DNA strands are shown as two lines: the thick one is the top strand and the thin one is the bottom strand. 1: A helicase (black triangle) separates the two complementary DNA strands, which are bound by SSB (grey circles). 2: Primers (lines with arrow heads) hybridize to the target region on the ssDNA template. 3: A DNA polymerase (squares with mosaic patterns) extends the primers hybridized on the template DNA. 4: Amplified products enter the next round of amplification.</p>

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<p><span style="font-size:16px">But there are several critical disadvantages exist in this method. Firstly, as it is still in its development stage, so the ratio of key components and the research about what enzymes synergitically work well are not clearly found yet. So the processivity of Uvrd and efficiency of denaturing speed is low. Secondly, since HDA requires a lot of enzymes, it needs the ready made kit of reagent which is way more expensive than reagent of PCR. Actually, these two disadvantages are main reasons that researchers still use PCR method to amplify the DNA instead of HDA.</span></p>

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<p><span style="font-size:26px"><strong>Improvement and&nbsp;Prospect</strong></span></p>

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<p><span style="font-size:16px">The first short, which is about ideal ratio and component of reagent can be overcome by an amount of research. Since this method is develpoed in 2007, so it now remains at its development stage. Further amount of research will find the ideal ratio and components of reagent so it will be matter of time. Second short is the cost of the reagent. This is basical problem because the low productivity of each component of reagent is higering the cost of the reagent. This should be improved by excogitating the efficient method of producing the key enzymes and components of HDA. If These shorts are overcome,&nbsp;It is clear that HDA has its own adcantages compare to other method. Then someday HDA is expected to be widley used and might replace the PCR method.</span></p>

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