title: A strategy for enhanced circular DNA construction efficiency based on DNA cyclization after microbial transformation.
abstract: BACKGROUND
  With the rapid development of synthetic biology, the demand for assembling multiple DNA (genes) fragments into a large circular DNA structure in one step has dramatically increased. However, for constructions of most circular DNA, there are two contradictions in the ligation/assembly and transformation steps. The ligation/assembly consists of two different reactions: 1) the ligation/assembly between any two pieces of a linear form DNA; 2) the cyclization (or self-ligation) of a single linear form DNA. The first contradiction is that the bimolecular ligation/assembly requires a higher DNA concentration while the cyclization favors a lower one; the second contradiction is that a successful transformation of a ligation/assembly product requires a relatively high DNA concentration again. This study is the first attempt to use linear plasmid and Cyclization After Transformation (CAT) strategy to neutralize those contradictions systematically.
  
  
  RESULTS
  The linear assembly combined with CAT method was demonstrated to increase the overall construction efficiency by 3-4 times for both the traditional ligation and for the new in vitro recombination-based assembly methods including recombinant DNA, Golden Gate, SLIC (Sequence and Ligation Independent Cloning) and Gibson Isothermal Assembly. Finally, the linear assembly combined with CAT method was successfully applied to assemble a pathway of 7 gene fragments responsible for synthesizing precorrin 3A which is an important intermediate in VB12 production.
  
  
  CONCLUSIONS
  The linear assembly combined with CAT strategy method can be regarded as a general strategy to enhance the efficiency of most existing circular DNA construction technologies and could be used in construction of a metabolic pathway consisting of multiple genes.
authors.affiliation: MOE Key Lab of Bioinformatics, Department of Biological Science and Biotechnology, School of Life Science, Tsinghua-Peking Center for Life Sciences, Tsinghua University, Beijing, 100084, China. guoyingying@973pha.org.
authors.forename: Ying-Ying
authors.initials: YY
authors.lastname: Guo
authors.affiliation: Synthenome.com, Dingley Village, VIC3172, Australia. errisy@gmail.com.
authors.forename: Zhen-Yu
authors.initials: ZY
authors.lastname: Shi
authors.affiliation: MOE Key Lab of Bioinformatics, Department of Biological Science and Biotechnology, School of Life Science, Tsinghua-Peking Center for Life Sciences, Tsinghua University, Beijing, 100084, China. fuxiaozhi@973pha.org.
authors.forename: Xiao-Zhi
authors.initials: XZ
authors.lastname: Fu
authors.affiliation: MOE Key Lab of Bioinformatics, Department of Biological Science and Biotechnology, School of Life Science, Tsinghua-Peking Center for Life Sciences, Tsinghua University, Beijing, 100084, China. chenjinchun@mail.tsinghua.edu.cn.
authors.forename: Jin-Chun
authors.initials: JC
authors.lastname: Chen
authors.affiliation: MOE Key Lab of Bioinformatics, Department of Biological Science and Biotechnology, School of Life Science, Tsinghua-Peking Center for Life Sciences, Tsinghua University, Beijing, 100084, China. wuqiong@mail.tsinghua.edu.cn.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Wu
authors.affiliation: MOE Key Lab of Bioinformatics, Department of Biological Science and Biotechnology, School of Life Science, Tsinghua-Peking Center for Life Sciences, Tsinghua University, Beijing, 100084, China. chengq@mail.tsinghua.edu.cn.|Center for Nano and Micro Mechanics, Tsinghua University, Beijing, 100084, China. chengq@mail.tsinghua.edu.cn.
authors.forename: Guo-Qiang
authors.initials: GQ
authors.lastname: Chen
mesh_terms: D003500:Cyclization; D004247:DNA / Q000378:metabolism*; D004270:DNA, Circular / Q000235:genetics*; D053858:Metabolic Networks and Pathways / Q000235:genetics*
chemical_list: D004270:DNA, Circular; D004247:DNA