Long-range PCR with a DNA polymerase fusion

STI PCR: An efficient method for amplification and de novo synthesis of long DNA sequences

Despite continuous improvements, it is difficult to efficiently amplify large sequences from complex templates using current PCR methods. Here, we developed a suppression thermo-interlaced (STI) PCR method for the efficient and specific amplification of long DNA sequences from genomes and synthetic DNA pools. This method uses site-specific primers containing a common 5' tag to generate a stem-loop structure, thereby repressing the amplification of smaller non-specific products through PCR suppression (PS). However, large target products are less affected by PS and show enhanced amplification when the competitive amplification of non-specific products is suppressed. Furthermore, this method uses nested thermo-interlaced cycling with varied temperatures to optimize strand extension of long sequences with an uneven GC distribution. The combination of these two factors in STI PCR produces a multiplier effect, markedly increasing specificity and amplification capacity. We also developed a webtool, calGC, for analyzing the GC distribution of target DNA sequences and selecting suitable thermo-cycling programs for STI PCR. Using this method, we stably amplified very long genomic fragments (up to 38 kb) from plants and human and greatly increased the length of de novo DNA synthesis, which has many applications such as cloning, expression, and targeted genomic sequencing. Our method greatly extends PCR capacity and has great potential for use in biological fields.

Long-Range PCR Amplification of DNA by DNA Polymerase III Holoenzyme from Thermus thermophilus

DNA replication in bacteria is accomplished by a multicomponent replicase, the DNA polymerase III holoenzyme (pol III HE). The three essential components of the pol III HE are the α polymerase, the β sliding clamp processivity factor, and the DnaX clamp-loader complex. We report here the assembly of the functional holoenzyme from Thermus thermophilus (Tth), an extreme thermophile. The minimal holoenzyme capable of DNA synthesis consists of α, β and DnaX (τ and γ), δ and δ′ components of the clamp-loader complex. The proteins were each cloned and expressed in a native form. Each component of the system was purified extensively. The minimum holoenzyme from these five purified subunits reassembled is sufficient for rapid and processive DNA synthesis. In an isolated form the α polymerase was found to be unstable at temperatures above 65°C. We were able to increase the thermostability of the pol III HE to 98°C by addition and optimization of various buffers and cosolvents. In the optimized buffer system we show that a replicative polymerase apparatus, Tth pol III HE, is capable of rapid amplification of regions of DNA up to 15,000 base pairs in PCR reactions.

Long-range PCR in next-generation sequencing: comparison of six enzymes and evaluation on the MiSeq sequencer

Long-range PCR remains a flexible, fast, efficient and cost-effective choice for sequencing candidate genomic regions in a small number of samples, especially when combined with next-generation sequencing (NGS) platforms. Several long-range DNA polymerases are advertised as being able to amplify up to 15 kb or longer genomic DNA. However, their real-world performance characteristics and their suitability for NGS remain unclear. We evaluated six long-range DNA polymerases (Invitrogen SequalPrep, Invitrogen AccuPrime, TaKaRa PrimeSTAR GXL, TaKaRa LA Taq Hot Start, KAPA Long Range HotStart and QIAGEN LongRange PCR Polymerase) to amplify three amplicons, with sizes of 12.9 kb, 9.7 kb, and 5.8 kb, respectively. Subsequently, we used the PrimeSTAR enzyme to amplify entire BRCA1 (83.2 kb) and BRCA2 (84.2 kb) genes from nine subjects and sequenced them on an Illumina MiSeq sequencer. We found that the TaKaRa PrimeSTAR GXL DNA polymerase can amplify almost all amplicons with different sizes and Tm values under identical PCR conditions. Other enzymes require alteration of PCR conditions to obtain optimal performance. From the MiSeq run, we identified multiple intronic and exonic single-nucleotide variations (SNVs), including one mutation (c.5946delT in BRCA2) in a positive control. Our study provided useful results for sequencing research focused on large genomic regions.

Long PCR-RFLP of 16S-ITS-23S rRNA genes: a high-resolution molecular tool for bacterial genotyping

AIMS

To perform a systematic evaluation of the applicability, validity and reliability of the long PCR-RFLP of 16S-ITS-23S rRNA genes for bacterial genotyping using both sequences retrieved from public genome databases and the experimental data obtained on bacterial cultures.

METHODS AND RESULTS

3301 Full-length sequences of 16S-ITS-23S rRNA genes were retrieved from 885 published bacterial genomes. Copy numbers of the whole set of 16S-ITS-23S rRNA genes per genome ranged from 1 (n = 161) to 14 (n = 4) with an average of 3.71. Their length varied greatly, from 4319 to 6568 bp with an average of 4952 bp. Computer-simulated RFLP analyses of the 16S-ITS-23S fragments flanked by the conserved primers 27F and 2241R suggested MspI, RsaI, HhaI and TaqI as the most appropriate enzymes for long PCR-RFLP analysis of the 16S-ITS-23S sequence. MspI was used to screen over 900 bacterial cultures isolated from the Huguangyan Maar Lake in southern China. An experimental sequencing of 16S rRNA genes of the isolates possessing a unique RFLP band pattern proved the broad applicability and high resolution of this approach.

CONCLUSIONS

These results indicate that long PCR-RFLP of 16S-ITS-23S rRNA genes is a potentially universal and reliable bacterial genotyping tool with a high resolution.

SIGNIFICANCE AND IMPACT OF THE STUDY

The methodology of long PCR-RFLP of 16S-ITS-23S rRNA genes will facilitate the exploration and tracing of cultivable microbial diversity in natural environments.