1. Get gene
You can copy it by RT-PCR, if you know the sequence. Alternatively, you can ask someone who has the cDNA, or purchase from a company.
2. Put gene into expression plasmid
There are three main types of expression systems; bacterial, insect and mammalian. The choice depends on your objective. Some systems can be inducible, some have built-in tag for detection or purification.
3. Transfect or transform the corresponding host with the expression plasmid
After transfection or transformation, you need to select with antibiotic for cells harboring the expression plasmid. You can then induce for protein expression.
4. Purify the recombinant protein
Various built-in tags will facilitate the purification of recombinant protein. For the bacterial expression system, the protein produced is often insoluble. Purification of recombinant protein is often done under denaturing conditions. The purified recombinant protein will require protein refolding before enzymatic activity can be determined.
Not affiliated with any company. Mention of a specifc product does not imply my endorsement of the product. No conflict of interest or guarantee to work on the advice given. Do as I say, not as I do. Not liable to the loss of your valuable samples.