Troubleshooting
Verify that the sequence following the T7 promoter contains the AG initiating sequence.
Control Reaction
The CLuc AG control template is a linearized plasmid containing the Cypridina luciferase gene under the transcriptional control of the T7 promoter. The initiating sequence has been changed to an AG by site-directed mutagenesis to be compatible with CleanCap Reagent AG. The size of the run-off transcript is ~1.76 kb. The control reaction, following the standard reaction protocol, should yield > 90 µg of RNA in 2 hours at 37°C.
If the control reaction is not working, there may be technical issues with the reaction set up. Repeat the reaction following the protocol exactly (thawing specified reagents to room temperature, setting the reaction up at room temperature, and adding the components in the exact order listed in the manual. Take every precaution to avoid RNase contamination.
The control plasmid sequence can be found within the DNA Sequences and Maps Tool under the name “pCMV-CLuc2 AG Control Plasmid”. The CLuc AG control template is generated by linearizing the plasmid with the restriction enzyme XbaI.
Low Yield of Full-length RNA
If the transcription reaction generates full-length RNA but yields are significantly lower than expected, it is possible that contaminants in the DNA template are inhibiting the RNA Polymerase or the DNA template concentration may be incorrect or too low. Additional purification of the DNA template may be required. Phenol:chloroform extraction is recommended (see template DNA preparation section).
Low yield of Short Transcript
High yields of short transcripts (< 300 nts) are achieved by extending incubation time and increasing the amount of template. Incubation of reactions up to 16 hours (overnight) or using up to 2 μg of template DNA can help achieve maximum yield.
RNA Transcript Smearing on Denaturing Gel
If the RNA appears degraded (smeared) on a denaturing agarose or polyacrylamide gel, the DNA template may be contaminated with RNase. DNA templates contaminated with RNase can affect the length and yield of RNA synthesized (smear below the expected RNA length). If the DNA template is contaminated with RNase, we recommend performing phenol:chloroform extraction followed by ethanol precipitation (see template DNA preparation section) and dissolving the DNA in nuclease-free water.
RNA Transcript of Larger Size than Expected
If the RNA transcript appears larger than the expected size on a denaturing gel when compared to a single-stranded RNA ladder, the plasmid DNA that is used for the template may not be completely digested. Even if small amounts of undigested circular plasmid DNA is present, T7 RNA Polymerase can produce large amounts of long transcripts. Check the digestion of the plasmid for complete digestion compared to a sample of undigested plasmid. If undigested plasmid is present repeat the restriction digest.
Alternatively, larger sized bands may be observed when the RNA is not completely denatured due to the presence of strong secondary structure.
RNA Transcript of Smaller Size than Expected
If denaturing gel analysis indicates the presence of smaller bands than expected it is most likely due to premature termination by T7 RNA Polymerase. Sequences that resemble T7 RNA Polymerase termination signals will cause premature termination. For GC-rich templates, or templates with known strong secondary structure, incubation at 42°C may improve the yield of full-length transcript.