Instability foreign protein

There is considerable evidence that foreign proteins are subject to a significant degree of degradation and instability in plant expression systems, both inside and outside of the cells. 

There have been many reports from several groups that plant culture medium is not conducive to protein stability, and that the retention of secreted proteins in culture media can be very poor [10, 11, 17, 40, 60, 63-66]. The mechanisms responsible for protein loss from plant culture media are not completely understood however, current indications are that multiple factors may be involved. Processes that have been proposed to affect foreign proteins in plant media include protein degradation due to protease activity [10, 17, 20, 38, 60, 65], protein instability due to defined or... 

Plasmid instability can arise when the foreign protein is toxic to the host cell. During rapid growth plasmids may be lost or the copy number reduced, allowing the non-recombinant cells to take over. As a... 

Bacillus subitilis Second best studied bacteria Gram positive—no outer membrane—excretes proteins Problem excreting some foreign proteins Makes large amounts and varieties of proteases (degrades proteins rapidly) More difficult to manipulate genetically owing to limited vectors and promoters Instability of plasmids more problematic than E. coli... 

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