ISOLATE II RNA Micro Kit

The columns supplied with the ISOLATE II kits may appear similar, but each type has been optimized to work within the buffer system supplied with the corresponding kit. The swapping of columns (or buffers) between kits may lead to no recovery of nucleic acid whatsoever, or at the very least severely impaired purification.

Interruption of the DNA/RNA extraction process is possible after the sample lysis only. It is possible to homogenize and lyse the samples and to store them in the freezer until use for RNA extraction. RNA clean up with a column cannot be interrupted and we recommend to avoid delays during the column purification process. If a delay is unavoidable the columns should be stored on ice.

The ISOLATE II RNA Micro Kit contains poly-A RNA for use as carrier RNA. We recommend to add 20 ng of carrier RNA to the sample lysate. This may improve the recovery of total RNA, but is overall dependent on sample type and RNA amount. The small amounts of poly-A RNA do not interfere with subsequent real-time PCR, even when oligo-dT is used as a primer for reverse transcription. If a poly-A RNA isolation is to be performed post isolation, carrier RNA should not be added. Other types of carrier RNA like ribosomal RNA or glycogen may be used instead, but are not supplied with this kit.

An increase of A230 values may be caused by different substances, like carbohydrates, peptides and phenol. A bad A230/A260 ratio in RNA samples is mostly due to a contamination with guanidinium thiocyanate which is present in several reagents used for RNA extraction, for instance in the lysis buffer. In contrast to a bad A280/A260 ratio it does not automatically reflect a bad RNA quality. Currently there is no consensus about a lower limit of this ratio and mostly a carry-over of guanidinium thiocyanate does not affect the reliability of downstream applications. Nevertheless, an extra washing step with RW2 would be helpful to avoid this problem. And it would be helpful to pipet the flow-through out of the collection tube, instead of pouring it off.

It is possible to use the ISOLATE II Plant DNA and RNA kits. The optimized lysis of these kits may be also useful for processing difficult to lyse bacteria and fungi in soil samples

For the optimal recovery of large RNA/DNA fragments it is necessary to optimize the elution step. To increase the recovery rate it would be helpful to use a larger volume for elution, incubate the column with the elution buffer prior to centrifugation and use repeated elution steps. To avoid excessive dilution it may be helpful to reapply the eluted fraction again.

Several possibilities exist. If you are using our column based extraction kit like the ISOLATE II RNA Mini kit it would be necessary to decrease the sample amount of such samples or to increase the amount of the lysis buffer RLY to prevent clogging of the columns. Another possibility would be a pre-extraction with TRIsure (BIO-38032) and to clean up the RNA containing aqueous phase with the column based ISOLATE II RNA kits. You should follow the TRIsure protocol up to the phase separation step. Then mix the aqueous phase with a volume of ethanol and load it onto the column. From there you should proceed with the regular ISOLATE II RNA Mini kit protocol.

These samples are treated as usual, just remove the RNAlater solution.

Agarose gel analysis of RNA samples can be both valuable and misleading. The pattern of bands on the gel can not only be indicative of the quality of the sample, but equally it can also only indicate that the gel tank, buffer or agarose is contaminated with RNase. A safer measure is to use a Bioanalyzer and look at the RIN value (RNA Integrity Number), which should be as close to 10 as possible, indicating that the RNA is not degraded. A spectrophotometer (ideally a microfluidic one) can also be used to determine the ratio of A260 to A280 for purity determination. All these methods give an idea of the quality of total RNA which tends to be dominated with rRNA and tRNA. It is not uncommon for an agarose gel to show an abundance of 18S and 23S rRNA but on analysis for there to be little of the transcript of interest. Ideally RNA quality control should include an assessment of the presence of common transcripts (from reference genes, such as GAPDH) using RT-PCR or RT-qPCR. If the yield of RNA is low, it is best to first check that all the solutions used and the equipment employed is largely free of RNase. Solutions should be prepared with the highest quality reagents available, preferably ones that have a certificate of analysis to show that they are free of DNase and RNase. If there is confidence that RNase contamination is at a minimum, then it may be worth ensuring that the sample is properly homogenised before lysis and to check a sample of the lysed material under a light microscope to ensure that all the cells are disrupted. RNA samples that have been contaminated with RNase (either during processing or those that have been sent from another lab) can be purified using the ISOLATE II RNA Micro Kit.