Small RNA Sample Prep Kit FAQs

Yes. However, we have seen high sample variability using some commercially available small RNA spin column purification methods, and validation of any purification method may be necessary. If purified small RNA is used as starting material, 10–50 ng should be used.

The protocol was optimized using 1 μg total RNA.

Yes, TruSeq cluster kits are backwards-compatible.

Reads longer than the small RNA molecule will sequence into the adapter. For this reason, we recommend sequencing for only enough cycles to cover the small RNAs of interest, or trimming the later cycles before aligning. The sequence that would need to be trimmed from the 3' end is given here for reference.

TGGAATTCTCGGGTGCCAAGGAACTCCAGTCACnnnnnnATCTCGTATGCCGTCTTCTGCTTG

This is the reverse complement of the index-specific primer sequence given in the Illumina Adapter Sequences Document, with the index sequence shown as nnnnnn.

This depends on the application. For expression profiling, 1–2M mapped reads is a generally accepted range. For discovery applications, an increase to 10–20M reads may be considered.

This depends on the aim of the experiment. For expression profiling projects, we do not recommend longer than 36 cycles of sequencing. The small RNA molecules are normally 15–30 bases long, and sequencing beyond this point only sequences the adapter. Eighteen cycles may be sufficient. For discovery projects, it may be worthwhile to do 40–50 cycles. This will sequence into the adapter, but the adapter sequence will be long enough to be unambiguously identified and removed even on longer small RNA molecules.

As with any molecular biology techniques, a change in protocol will give a change in absolute results. We do not recommend comparing absolute counts (or counts normalized to total counts) between different preparation protocols. However, comparison of fold change between the two protocols should yield good correlation.