> For the complete documentation index, see [llms.txt](https://knowledge.illumina.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://knowledge.illumina.com/library-preparation/rna-library-prep/library-preparation-rna-library-prep-reference_material-list/000002864.md).

# Types of small RNA and the need for a separate small RNA kit

**Most common types of small RNA:**

| **Abbreviation** | **Name**              | **Length**                          | **Description**                     |
| ---------------- | --------------------- | ----------------------------------- | ----------------------------------- |
| miRNA            | microRNA              | 18-25 nt                            | Inhibit translation of mRNA.        |
| siRNA            | small interfering RNA | 20-25 nt (longer has been reported) | Cleave mRNA                         |
| piRNA            | Piwi-interacting RNA  | 24-31 nt                            | Silence transposons in the germline |

**Why is a separate small RNA kit required?**\
The small RNAs are too small to be captured by the Total RNA and mRNA library preparation kits. Library fragments generated from such small RNAs are not faithfully retained during bead clean-up steps.

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| *For any feedback or questions regarding this article (Illumina Knowledge Article #2864), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000002864%20-%20Library%20Preparation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |


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