# Why your AP-site DNA templates slip when you least expect it - facts

Canonical page: https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect
Type: Lab article

## TL;DR

HMCES cross-links to AP sites in single-stranded DNA, and that cross-link drives the biology. Even trimmed by SPRTN to a five-amino-acid peptide, it still acts.

## Facts Index

| Fact ID | Category | Entity | Attribute | Value | Source | Evidence |
|---|---|---|---|---|---|---|
| why-ap-site-dna-templates-slip-when-least-expect:title | identity | Why your AP-site DNA templates slip when you least expect it | title | Why your AP-site DNA templates slip when you least expect it | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect |
| why-ap-site-dna-templates-slip-when-least-expect:published | identity | Why your AP-site DNA templates slip when you least expect it | published | 2026-08-17 | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect |
| why-ap-site-dna-templates-slip-when-least-expect:author | identity | Why your AP-site DNA templates slip when you least expect it | author | PreppinPeppers Editorial Team | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect |
| why-ap-site-dna-templates-slip-when-least-expect:topics | identity | Why your AP-site DNA templates slip when you least expect it | topics | peptide research, Research, study | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect |
| why-ap-site-dna-templates-slip-when-least-expect:summary | content | Why your AP-site DNA templates slip when you least expect it | summary | HMCES cross-links to AP sites in single-stranded DNA, and that cross-link drives the biology. Even trimmed by SPRTN to a five-amino-acid peptide, it still acts. | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect |
| why-ap-site-dna-templates-slip-when-least-expect:section-1 | content | Why your AP-site DNA templates slip when you least expect it | section | What HMCES Does | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect |
| why-ap-site-dna-templates-slip-when-least-expect:section-2 | content | Why your AP-site DNA templates slip when you least expect it | section | What HMCES actually does to an AP site | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect |
| why-ap-site-dna-templates-slip-when-least-expect:section-3 | content | Why your AP-site DNA templates slip when you least expect it | section | The surprising result: it's the cross-link, not the peptide length | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect |
| why-ap-site-dna-templates-slip-when-least-expect:section-4 | content | Why your AP-site DNA templates slip when you least expect it | section | Why this matters at the bench | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect |
| why-ap-site-dna-templates-slip-when-least-expect:section-5 | content | Why your AP-site DNA templates slip when you least expect it | section | The bigger picture | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect |
| why-ap-site-dna-templates-slip-when-least-expect:source-www-biorxiv-org | source | Why your AP-site DNA templates slip when you least expect it | cites | this coverage at bioRxiv → - www.biorxiv.org | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://www.biorxiv.org/content/10.64898/2026.08.14.744967v1?rss=1 |
| why-ap-site-dna-templates-slip-when-least-expect:source-pmc-ncbi-nlm-nih-gov | source | Why your AP-site DNA templates slip when you least expect it | cites | Yudkina et al., Int J Mol Sci 2023: Bypass of Abasic Site-Peptide Cross-Links by Human Repair and Translesion DNA Polymerases - pmc.ncbi.nlm.nih.gov | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://pmc.ncbi.nlm.nih.gov/articles/PMC10341727/ |
| why-ap-site-dna-templates-slip-when-least-expect:product-gansulin-metal-peptide-pen | products | Why your AP-site DNA templates slip when you least expect it | references product | Gansulin Pen · Reusable Click-Dial, 3 ml (1-60 Units) | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://www.preppinpeppers.com/products/gansulin-metal-peptide-pen |
| why-ap-site-dna-templates-slip-when-least-expect:product-gansulin-3ml-cartridge | products | Why your AP-site DNA templates slip when you least expect it | references product | Gansulin-Compatible 3 ml Glass Cartridge for Pens (10-Pack) | Lab article (https://www.preppinpeppers.com/blogs/the-lab/why-ap-site-dna-templates-slip-when-least-expect) | https://www.preppinpeppers.com/products/gansulin-3ml-cartridge |

## FAQ

### Does trimming HMCES off the AP site make bypass cleaner?

No. In Xenopus egg extracts, mutagenicity of HMCES-DPC bypass is insensitive to how much SPRTN has proteolyzed the cross-link; only cross-link formation itself matters, because it locks the AP site in a dynamic ring-opened state.

### Why does the base 5' of the AP site change the mutation spectrum?

The cross-link increases conformational flexibility of the template, allowing the 5' template nucleotide to slip into the polymerase active site and direct insertion opposite the adducted AP site, producing context-dependent mutations.

### Should I worry about HMCES in my cell extract lesion-bypass assay?

Yes. Any extract or lysate containing HMCES will form thiazolidine cross-links to true abasic sites in ssDNA, altering polymerase readouts compared with a synthetic THF or dSpacer mimic that cannot be cross-linkable.

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