---
title: "Optimizing E. coli Spike-in DNA for CUT&RUN Normalization"
slug: "optimizing-e-coli-spike-in-dna"
description: "Learn how to optimize E. coli spike-in DNA for CUT&RUN normalization to improve data quality, consistency, and sample comparison."
updated: 2026-09-23T22:09:32Z
published: 2026-09-23T22:09:32Z
canonical: "support.epicypher.com/optimizing-e-coli-spike-in-dna"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://support.epicypher.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Optimizing E. coli Spike-in DNA concentration

We recommend adding *E. coli* Spike-in DNA ([EpiCypher 18-1401](https://www.epicypher.com/product/cutana-e-coli-spike-in-dna/)) to all CUT&RUN reactions for sequencing normalization. The spike-in DNA is added following pAG-MNase digestion, as part of the Stop Buffer. The major goal is for *E. coli* DNA to comprise ~1% (0.2-5%) of total sequencing reads, which provides ample reads for normalization without overtaking the dataset.

The amount of *E. coli* DNA added per reaction should consider the number of cells per reaction, processing conditions (cross-linking vs. native), and target abundance. Thus, optimization may be required.

**For reactions using 500,000 cells**, add 0.5-1 ng *E. coli* Spike-in DNA. This amount of spike-in DNA reflects our standard CUTANA™ CUT&RUN protocol, and works for most cell types, targets, and processing conditions.

**For lower cell numbers,** the spike-in amount should be scaled linearly from the 500,000 cell baseline. For instance, for 50,000 cells, use 0.05-0.1 ng *E. coli* Spike-in DNA.

Note that low-abundance targets often have a higher percentage of total sequencing reads assigned to *E. coli* DNA, while high-abundance targets may have a lower percentage of spike-in reads. As a result, a range of spike-in read coverage is acceptable (0.2-5%). This is illustrated in **Table 1** using our recommended CUTANA CUT&RUN control antibodies, which include low-abundance (H3K4me3) and high-abundance (H3K27me3) targets, as well as a negative control (IgG). Each reaction was performed using 500,000 K562 cells and spiked with 0.5 ng or 1.0 ng *E. coli* DNA. Observations are as follows:

- **IgG:** The IgG negative control typically has a high percentage of reads attributed to *E. coli* DNA. In this experiment, 0.5 ng spike-in DNA was preferred (bold blue text), as it brings the percentage of *E. coli* reads below 5%.
- **H3K4me3:** This low-abundance target needs only 0.5 ng spike-in DNA to generate the appropriate number of reads for normalization. However, 1.0 ng is also acceptable.
- **H3K27me3:** As a high-abundance target, H3K27me3 generates more unique sequencing reads, and thus has a lower percentage of reads assigned to *E. coli* DNA. In order to generate adequate reads for sequencing normalization, 1.0 ng of spike-in DNA is recommended (blue text).

| **E. *coli* Spike-in DNA** | **Target** | Total reads | *E. coli* reads | % *E. coli* reads |
| --- | --- | --- | --- | --- |
| 0.5 ng | **IgG** | **3,644,233** | **155,549** | **4.27%** |
| **H3K4me3** | **3,121,112** | **42,210** | **1.35%** |
| H3K27me3 | 5,254,299 | 8,511 | 0.16% |
| 1.0 ng | IgG | 2,569,291 | 241,645 | 9.41% |
| H3K4me3 | 3,127,912 | 147,565 | 4.72% |
| **H3K27me3** | **9,650,258** | **22,419** | **0.23%** |

**Table 1:** EpiCypher *E. coli* Spike-in DNA (0.5 and 1.0 ng) was added to CUT&RUN samples using 500,000 K562 cells enriched for a low-abundance target (H3K4me3, EpiCypher 13-0060), a high-abundance target (H3K27me3, EpiCypher 13-0055) and an IgG negative control (EpiCypher 13-0042). Total numbers of paired-end sequencing reads, reads aligned to *E. coli,* and percentage of total sequencing reads aligned to *E. coli* spike-in DNA are shown. Bold blue text highlights the spike-in amounts recommended for each target.