Synthesis of Complete Gene,Overlapping Segments,Concerned Gene,Gene Synthesis,Bacillus Thuringiensis

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	Synthesis of Complete Gene - It is not possible to synthesize the entire gene directly, but oligonucleotides of up to about 50 nucleotides are rapidly synthesized. One of the strategies for synthesizing the complete gene is to synthesize short stretches of the two DNA strands in such a way that each segment of one strand overlaps two segments of the other strands. Therefore, the segments of the two strands become properly aligned due to complementary base pairing among the various segments of the two strands. For example, the somatostatin gene was synthesized as eight overlapping segments of the two strands. Similarly, the 514 bp long interferon gene was assembled from 66 short fragments representing the two strands.
However, it is now far more convenient, cheap and rapid to isolate the concerned gene from the genome or from total mRNA using PCR; chemical synthesis is used to only produce the two primers specific to the 3' -ends of the gene.But synthesis of the complete gene sometimes becomes necessary even when the original gene is available. This need arises because of the desirability of introducing extensive and specific changes in the base sequence of the gene for one or the other reason, e.g., to increase codon usage in the new genetic background (new host or organism). One of the important examples of such a gene synthesis concerns the cry genes of Bacillus thuringiensis, which encodes the famous insecticidal crystal (Cry) proteins.