Vectors that employ a tetracycline based promoter also enable tight control of expression that is independent of the host strain or metabolism, and dictated our initial construction of the bacterial IgG cassette in this vector Previous experiments using the Tet repressor had shown that below 50 ng/ml, concentration of inducer becomes limiting although the relationship between expression yield and inducer is not linear. We therefore carried out an induction at the manufacturer��s recommended concentration of 200 ng/ml. Other methods which can reduce NMS-P118 translation rates include induction of expression when the bacteria are approaching late log phase. This was used previously by Mazor et al for the production of full-length IgG. Accordingly, aside from the standard OD600 0.6 for induction we also tested expression when induction was started with culture at OD600 1.0. Use of low copy number plasmids has also been shown to decrease translation rate. In the course of constructing our expression vector, we generated both a low copy and high copy version of our expression plasmid, by addition of a single base pair mutation in the origin of replication. The difference in copy number between the high and low copy plasmids, based on miniprep DNA yields, is estimated to be approximately eight- to ten- fold. To analyze expression induced by our new construct, we employed five different full length IgGs. One was a chimeric antibody derived from the (R)-(-)-Modafinic acid anti-dengue mouse monoclonal hybridoma 4G2; and the other four fully human antibodies isolated from a na? ��ve human phage display library; of which two were raised against Clostridium perfringens epsilon toxin and the other two against Bacillus anthracis protective antigen. Studies were carried out in small scale shake cultures with various combinations of different concentrations of inducer, induction at different optical densities and using either high or low copy expression vector, as indicated. In order to prevent leakage of expressed antibody from the periplasm during growth by mechanical sheer, which commonly occurs during periplasmic expression in the HB2151 E. coli strain, protein expression was carried out in non-baffled flasks at a slower shaking speed of 120 rpm.