In: Biology
The gene for human growth hormone (hGH) is isolated from human pituitary gland.Insertion of whole hGH gene into plasmid vector and cloning in bacteria ( E.coli ) results into production of biologically inactive hormone because bacteria can translate the region of gene that are not translated in human thereby producing a prehormone containing an extra 26 aminoacids which might be difficult to remove.
So at first,segment of gene that codes for the first 24 aminoacids of hormone is constructed chemically from blocks of nucleotide. next mRNA for hGH is isolated from human pituitary gland tissue. Then using reverse transcriptase enzyme complimentary DNA (cDNA) is synthesized from mRNA. This full gene is cut with restriction endonuclease enzyme to remove first 24 gene.Then the synthetic gene (gene for first 24 aminoacids) and cDNA are joined in order to obtain full gene with its own initiation codon (AUG). This full gene is ligated into a restriction site just downstream of Lac; promotor/operator region of the expression vector.