Study of stability of recombinant plasmid containing the coding sequence of the human growth hormone in Escherichia coli cells. .

Escherichia coli is one of the most widely used hosts for production of heterologous proteins. Some non-glycosylated proteins are biologically active, being prokaryotic expression systems preferred in their production. One example of these recombinant proteins is the human growth hormone (hGH), a pituitary-derived polypeptide with a wide range of biological functions including protein synthesis, cell proliferation and therapeutic applications in different treatments (TABANDEH, 2004). The use of plasmids as vector for the production of recombinant proteins is essential for example, to produce high value proteins such as human growth hormone, in sufficient amounts in industrial production line and research. In commercial production with recombinant microorganisms, one of the most important problems is plasmid instability, a tendency of the transformed cells to loose their engineered properties because of changes to, or loss of, plasmids. Instability of plasmids can result in a significant loss in productivity, being important to know whether they have structural and segregational stability (ZHANG, 1996), important factor deterrnining either success or failure in fields of plasmid application. Structural stability describes the correct replication during cultivation of plasmid bearing cells leading to a non-altered base sequence of the plasmid. When plasmids are passed on to the daughter cells, so that each daughter cell has at least one copy, the system shows segregational plasmid stability (FRIEHS, 2004). The plasmid stability test determines what proportion of the cells maintain the target plasmid and the ability to express the target protein. In the present study we produce the human growth hormone (hGH) using Escherichia coli and we are particularly interested in the establishment of a protocol to study the stability