Variation of magnesium concentration
Figure 2: Impact of Mg(OAc)2 addition during cell-free expression of Luciferase. The regular feeding every 20 min with 100mM MgOAc2 shows an increase of expression to half of that of the commercial kit.
At first, we investigated the influence of magnesium acetate (Mg(OAc)2) on our reaction. Kim et al.1) describe an enhancement of cell-free expression by regular addition of small amounts of Mg. We performed expression experiments where reactions were fed with Mg(OAc)2 while others were not. The repeated addition of 100 nmol of magnesium every 20 minutes during the reaction was found to increase expression levels and was therefore implemented for future experiments. Feeding was performed by pipetting 0.5 μl of a 10 μM magnesium acetate solution into the reaction tube without letting it cool down. Positive effects towards expression were immediately visible in a subsequently conducted luciferase assay (see figure 2). However, the actual impact of feeding varied a lot in the experiments, even among reactions with the same components.