# mRNA caps accumulate in stress granules and are essential for their formation

## TL;DR

This study shows that mRNA caps are crucial for forming stress granules, which help cells survive stress by protecting mRNA.

## Contribution

The study reveals that mRNA caps are essential for stress granule formation and are enriched in these structures.

## Key findings

- mRNA Cap1 and non-canonical caps are predominantly enriched in stress granules.
- Knockdown of RNMT disrupts stress granule formation under various stress conditions.
- mRNAs partition into stress granules through interactions between caps and proteins.

## Abstract

Stress granules (SGs) are essential cytoplasmic, membraneless organelles that form in response to cellular stress, functioning to prevent mRNA translation and protect mRNA from damage. However, the mechanism of SG formation remains largely unknown. Here, utilizing a systems-level technique for quantification of RNA cap epitranscriptome, we found that mRNA Cap1 and non-canonical caps are predominantly enriched in SGs, with the composition of mRNA caps in SGs of mammalian cells differing between different stress conditions. Knockdown of RNA guanine-7-methyltransferase (RNMT) and phosphorylated CTD interacting factor 1(PCIF1) both resulted in substantial changes in the content and composition of mRNA caps and RNMT knockdown caused failure of SG formation under different stress conditions. Furthermore, proteomic, Co-IP and confocal immunofluorescence analysis of these knockdown cells and SGs revealed that mRNAs partition into SGs through cap-protein interactions. These findings collectively revealed the significant role of mRNA cap in SG formation and stress response in mammalian cells.

The online version contains supplementary material available at 10.1007/s00018-025-05947-8.