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 q uantitate 70S ribosomes, the 30S and 50S subunits, and tRNA in one single a nalytical procedure. The method was applied to an investigation of the effe ct of Vitreoscilla hemoglobin (VHb) on the translational machinery of the r ecombinant Escherichia coli cells. The number of active 70S ribosomes per c ell increased dramatically, more than 2-fold, as did also the tRNA levels f or 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 t hat VHb promotes the level of translational components. There should be man y other cases in bioengineering where it is important to relate the protein production level in a bioreactor to the ribosome and tRNA levels.