For protein production, the gene of interest is inserted in an expression vector and introduced into a suitable host for expression. But how is the gene of interest for the desired protein isolated from the organism which possesses it?
One way could be to synthetically make the DNA sequence coding for that protein. Another could be to identify the gene of interest from a pre-existing genomic library or cDNA library of that organism. Are they the only methods?
The organism's entire genome could be taken and cleaved with restriction endonucleases, and a Southern blotting technique (i.e. electrophoresis followed by probe hybridisation and autoradiography) could be used to screen the gene of interest from the fragments produced. Of course, for this the gene sequence must be known beforehand, in order to synthesise the probe. Is this method also adopted? It seems inefficient - given that the fragments are assumed to have the intact gene of interest, and the gene should have been sequenced beforehand.