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Artificial gene synthesis is a method in synthetic biology that is used to create artificial genes in the laboratory. Currently based on solid-phase DNA synthesis, it differs from molecular cloning and polymerase chain reaction (PCR) in that the user does not have to begin with preexisting DNA sequences. Therefore, it is possible to make a completely synthetic double-stranded DNA molecule with no apparent limits on either nucleotide sequence or size. The method has been used to generate functional bacterial or yeast chromosomes containing approximately one million base pairs. Recent research also suggests the possibility of creating novel nucleobase pairs in addition to the two base pairs in nature, which could greatly expand the possibility of expanding the genetic code. Synthesis of the first complete gene, a yeast tRNA, was demonstrated by Har Gobind Khorana and coworkers in 1972. Synthesis of the first peptide- and protein-coding genes was performed in the laboratories of Herbert Boyer and Alexander Markham, respectively.〔 Commercial gene synthesis services are now available from numerous companies worldwide, some of which have built their business model around this task.〔For example, the company DNA 2.0 was established in 2003 in Menlo Park, CA as a "synthetic genomics company" ((quotated page )).〕 Current gene synthesis approaches are most often based on a combination of organic chemistry and molecular biological techniques and entire genes may be synthesized "de novo", without the need for precursor template DNA. Gene synthesis has become an important tool in many fields of recombinant DNA technology including heterologous gene expression, vaccine development, gene therapy and molecular engineering. The synthesis of nucleic acid sequences is often more economical than classical cloning and mutagenesis procedures. ==Gene optimization== While the ability to make increasingly long stretches of DNA efficiently and at lower prices is a technological driver of this field, increasingly attention is being focused on improving the design of genes for specific purposes. Early in the genome sequencing era, gene synthesis was used as an (expensive) source of cDNAs that were predicted by genomic or partial cDNA information but were difficult to clone. As higher quality sources of sequence verified cloned cDNA have become available, this practice has become less urgent. Producing large amounts of protein from gene sequences (or at least the protein coding regions of genes, the open reading frame) found in nature can sometimes prove difficult and is a problem of sufficient impact that scientific conferences have been devoted to the topic. Many of the most interesting proteins sought by molecular biologists are normally regulated to be expressed in very low amounts in wild type cells. Redesigning these genes offers a means to improve gene expression in many cases. Rewriting the open reading frame is possible because of the degeneracy of the genetic code. Thus it is possible to change up to about a third of the nucleotides in an open reading frame and still produce the same protein. The available number of alternate designs possible for a given protein is astronomical. For a typical protein sequence of 300 amino acids there are over 10150 codon combinations that will encode an identical protein. Using optimization methods such as replacing rarely used codons with more common codons sometimes have dramatic effects. Further optimizations such as removing RNA secondary structures can also be included. At least in the case of ''E. coli'', protein expression is maximized by predominantly using codons corresponding to tRNA that retain amino acid charging during starvation. Computer programs written to perform these, and other simultaneous optimizations are used to handle the enormous complexity of the task.〔(【引用サイトリンク】 title=Protein Expression )〕 A well optimized gene can improve protein expression 2 to 10 fold, and in some cases more than 100 fold improvements have been reported. Because of the large numbers of nucleotide changes made to the original DNA sequence, the only practical way to create the newly designed genes is to use gene synthesis. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Artificial gene synthesis」の詳細全文を読む スポンサード リンク
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