Expression of Vitreoscilla hemoglobin in Escherichia coli enhances ribosome and tRNA levels:: A flow field-flow fractionation study

Asymmetrical flow field-flow fractionation (FFF) was used to separate and quantitate 70S ribosomes, the 30S and 50S subunits, and tRNA in one single analytical procedure. The method was applied to an investigation of the effect of Vitreoscilla hemoglobin (VHb) on the translational machinery of the recombinant Escherichia coli cells. The number of active 70S ribosomes per cell increased dramatically, more than 2-fold, as did also the tRNA levels for the VHb-expressing strain relative to VHb-negative control at the end of a 30-h fed-batch cultivation. This was accompanied by a corresponding 61% increase of a cloned marker enzyme activity. The results clearly indicate that VHb promotes the level of translational components. There should be many other cases in bioengineering where it is important to relate the protein production level in a bioreactor to the ribosome and tRNA levels.