tRNA Purification

The biggest issue we initially faced in developing Next vivo was determining how we could purify tRNA quickly and efficiently. The solution we decided upon was an adapted MS2 RNA co-purification combined with a subsequent incubation with RNase H and a DNA oligo that would selectively cleave and release a tRNA of the proper size. For more information on the design, see the <a href="http://2017.igem.org/Team:Lethbridge/Design#anchor5" id="pageLink"> tRNA purification</a> section here.

Both the tRNA^phe-MS2 aptamer construct and MS2BP were overexpressed individually in E. coli BL21-Gold (DE3) cells. Upon which time the cells were lysed, the lysate combined, and applied to a Nickel Sepharose affinity column. In order to cleave the RNA, 1 µM of DNA oligo was added to the column, as well as varying amounts of RNase H. Incubation times on the column with RNase H and DNA oligo varied from 2 hours (Figure 3) to 12 hours (Figure 4), and the amount of RNase H used varied from 10 units to 100 units (Figure 3 and 4). Based upon the varied conditions, a longer incubation time had the greatest effect on tRNA cleavage efficiency with units of RNase H being optimal between the range of 5-50. With these improvements from our initial attempt at tRNA cleavage we successfully purified tRNA^Phe, as shown in Figure 4.

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Figure 3 - Preliminary tRNA^Phe Purification. 12% 8M urea PAGE run for 45 mins at 300 V. All concentrated fractions were phenol chloroform extracted, ethanol precipitated and re-suspended in 30 µL of ddH₂O. Lanes are as follows: 1- tRNA fraction with 20 units of RNase H added; 2- concentrated tRNA fraction 20 units of RNase H added; 3- concentrated MS2 fraction 1 20 units of RNase H added; 4- concentrated MS2 fraction 2 20 units of RNase H added; 5- tRNA standard (76 nt).

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Figure 4 - Successful tRNA^Phe Purification. 12% 8M urea PAGE run for 45 mins at 300 V. All fractions were phenol chloroform extracted, ethanol precipitated and re-suspended in 30 µL of ddH₂O. Lanes are as follows - 1- MS2 fraction 25 units of RNase H added; 2- tRNA fraction 25 units of RNase H added; 3- MS2 fraction 50 units of RNase H added; 4- tRNA fraction 50 units of RNase H added; 5- MS2 fraction 100 units of RNase H added; 6- tRNA fraction 100 units of RNase H added; 7- MS2 fraction 10 units of RNase H added; 8- tRNA elution 10 units of RNase H added; 9- tRNA standard (76 nt).