Cell cycle clock controls RNA methylation through a hidden ubiquitin code

Every time a cell divides, it must copy its DNA, duplicate its organelles and, less famously, recalibrate the chemical decoration of its messenger RNA. One of the most consequential of these decorations is N6-methyladenosine, or m6A, the most abundant internal modification in mammalian mRNA, which influences nearly every stage of an RNA transcript’s life, from processing and export to translation and decay. Although researchers have long known that global m6A levels shift as cells progress through the cycle of growth and division, the machinery that imposes this timing has remained obscure. A new study published in Nature Chemical Biology now identifies a surprising regulator: a RING-finger ubiquitin ligase known as RLIM, which tags the m6A-writing enzyme METTL14 with an unusual form of ubiquitin that changes the writer’s behavior without changing how much of it exists in the cell.

The work, led by Jianzhao Liu and Xin-Hua Feng of Zhejiang University together with colleagues at Soochow University and other Chinese institutions, began with a simple but technically demanding question: is METTL14, the scaffold subunit of the m6A methyltransferase complex, itself chemically modified? Using immunoprecipitation followed by immunoblotting in HEK293T and HeLa cells, the team found that METTL14, but not its catalytic partner METTL3 nor the regulatory subunit WTAP, is robustly ubiquitinated. Ubiquitin is best known as a destruction tag: chains linked through its lysine-48 residues deliver proteins to the proteasome. But ubiquitin can be assembled into eight distinct chain types, and several of them, including K27-linked chains, are thought to modulate protein interactions and localization rather than stability. When the researchers restricted cellular ubiquitin to single-linkage variants, METTL14’s modification turned out to be dominated by exactly this noncanonical K27 linkage.

Mass spectrometry then mapped the modification to specific lysine residues on METTL14, including lysines 148 and 278, positions that sit near the interfaces through which METTL14 grips its partners. To find the enzyme responsible, the team pulled down METTL14 and searched its associated proteins for candidate E3 ubiquitin ligases. The screen converged on RLIM, also known as RNF12, a RING-domain ligase first characterized as a corepressor of LIM homeodomain transcription factors. RLIM’s catalytic activity proved essential: a ligase-dead H569A/C572A mutant or a construct lacking the RING domain entirely failed to promote METTL14 ubiquitination, whereas wild-type RLIM drove robust K27-linked tagging in cells and in reconstituted in vitro reactions with defined E1 and E2 enzymes.

What makes this finding conceptually striking is what the ubiquitin mark does not do. RLIM knockout did not alter METTL14 protein abundance, and immunofluorescence showed that METTL14 still entered the nucleus normally in cells lacking RLIM. Instead, the modification acted on function. In vitro methylation assays demonstrated that K27-ubiquitinated METTL3–METTL14 complexes were markedly impaired in their ability to methylate RNA substrates. Two mechanisms accounted for the deficit. First, structural modeling and biochemical assays indicated that ubiquitin conjugated at lysine 278 distorts the loop regions at the METTL3–METTL14 interface, weakening the heterodimer that constitutes the active writer. Second, electrophoretic mobility shift assays and microscale thermophoresis showed that ubiquitinated or ubiquitination-mimicking complexes bound RNA less tightly, reducing substrate engagement. A split Nano-Luciferase reporter confirmed in living cells that RLIM expression disrupts METTL3–METTL14 association. In other words, RLIM acts as a rheostat on the writer’s activity rather than a trigger for its disposal.

The physiological consequence was visible across the transcriptome. MeRIP-seq and RNA-seq comparisons of control and RLIM-knockout cells revealed widespread hypermethylation of mRNA m6A peaks when RLIM was absent, with the affected transcripts enriched for genes governing the G2/M transition of the cell cycle. Consistent with known links between m6A and mRNA stability, hypermethylated transcripts in RLIM-knockout cells showed shortened half-lives, and many overlapped with binding targets of the m6A reader YTHDF2, which routes methylated transcripts toward degradation. Representative loci such as E4F1 and RHOB, both implicated in cell-cycle control, gained m6A and lost stability when RLIM was removed, and MeRIP-qPCR validated these changes independently.

The cell-cycle connection then became explicit. When the researchers synchronized cells by double thymidine block and released them, they observed coordinated periodic oscillations in three quantities: transcriptome-wide m6A levels, the intensity of K27-linked ubiquitin on METTL14, and RLIM protein abundance. RLIM knockout arrested cells at the G2/M boundary, an effect that could be rescued by knocking down METTL14, placing RLIM upstream of the writer in a pathway that governs mitotic entry. Measurements of global m6A-to-A ratios by LC-MS/MS across G1/S, S, G2, M and G1 phases confirmed that the methylation landscape rises and falls with the cycle, and immunofluorescence for phospho-histone H3 showed RLIM levels dropping precisely in mitotic cells.

The mechanism behind RLIM’s own oscillation turned out to be a classic mitotic kinase. The CDK1–cyclin B1 complex, the master switch for mitotic entry, physically associated with RLIM and phosphorylated it. Phosphatase treatments and Ser/Thr-to-Ala mutant analysis identified the phosphorylation sites responsible, and these modifications triggered RLIM to ubiquitinate itself with K48-linked chains, condemning it to proteasomal degradation. Blocking CDK1 or cyclin B1 by RNA interference stabilized RLIM, while proteasome inhibition with MG132, but not lysosomal inhibition with chloroquine, rescued the protein. This arrangement creates an elegant feedback loop: as CDK1–cyclin B1 surges at G2/M, it destroys RLIM, which releases METTL14 from inhibitory ubiquitination, allowing the writer complex to reassemble and retune the m6A landscape for the next phase of the cycle.

To test whether this axis matters beyond cultured cells, the team turned to animal and clinical models. In mice with Rlim deleted specifically in the myeloid lineage, bone marrow cells showed elevated m6A methylation on cell-cycle and differentiation genes, and flow cytometry revealed perturbed hematopoietic populations, effects that intensified after vesicular stomatitis virus infection. Endogenous METTL14 in these marrow cells lost its K27-linked ubiquitination, confirming the pathway operates in primary tissue. The researchers also examined MOLM-13, an acute myeloid leukemia cell line, where RLIM knockdown altered cell-cycle distribution and myeloid differentiation markers and reduced colony formation. Most compellingly, samples from patients with acute monocytic leukemia, collected through collaborating hospitals in Suzhou, displayed dysregulation of the RLIM–METTL14 axis, linking the molecular circuit to human disease.

The study’s broader significance lies in expanding the vocabulary of epitranscriptomic regulation. For a decade, the m6A writer has been viewed largely as a stable assembly whose output is tuned by accessory proteins, substrate availability and chromatin state. This work adds a temporal dimension: a cell-cycle-programmed, noncanonical ubiquitin code that switches the writer’s activity on and off without touching its concentration. Because K27-linked chains are increasingly recognized as scaffolds for protein–protein interactions in cell-cycle and quality-control pathways, the finding suggests that other RNA-processing enzymes may carry similar non-degradative marks awaiting discovery. It also reframes ubiquitin ligases, traditionally studied in the context of protein turnover, as direct modulators of the epitranscriptome.

Therapeutically, the implications are tantalizing but preliminary. Acute myeloid leukemia has already emerged as a disease exquisitely sensitive to m6A dosage, with the writer METTL3, the erasers FTO and ALKBH5, and the reader YTHDF2 each implicated in leukemic self-renewal. The new axis adds RLIM, and the CDK1–cyclin B1 switch that controls it, to the list of potential intervention points. CDK1 inhibitors are already in clinical use for other indications, raising the possibility that modulating RLIM stability could tune m6A levels in leukemia cells. For now, the study stands as a demonstration that the cell’s division clock reaches deep into its RNA chemistry, and that a ubiquitin tag once dismissed as obscure may be one of the hands on that clock.

Subject of Research: Cell-cycle-regulated noncanonical K27-linked ubiquitination of METTL14 controlling mRNA m6A methylation

Article Title: Cell-cycle-driven noncanonical ubiquitination of METTL14 orchestrates RNA methylation

Article References: Cao, J., Ying, X., Zhou, L., Zhang, Q., Huang, C., Dai, T., Shu, X., Gao, M., Mi, Y., Wu, X., Wang, F., Zhang, L., Zhou, F., Feng, X.-H., & Liu, J. (2026). Cell-cycle-driven noncanonical ubiquitination of METTL14 orchestrates RNA methylation. Nature Chemical Biology. https://doi.org/10.1038/s41589-026-02328-5

Image Credits: AI Generated

DOI: 10.1038/s41589-026-02328-5

Keywords: m6A, METTL14, RLIM, ubiquitination, K27-linked ubiquitin, cell cycle, CDK1, cyclin B1, epitranscriptomics, RNA methylation, acute myeloid leukemia, post-translational modification