Cell-cycle-driven noncanonical ubiquitination of METTL14 orchestrates RNA methylation.

The precise temporal control of global mRNA methylation during the cell cycle is critical, yet the underlying mechanism remains unknown. Here we elucidate a noncanonical ubiquitination-mediated regulatory mechanism whereby RLIM deposits predominantly K27-linked ubiquitin (K27-Ub) on the m6A methyltransferase METTL14 in a cell-cycle-programmed manner. This modification modulates enzymatic activity by controlling METTL3-METTL14 complex assembly and RNA substrate engagement, independent of protein stability. We discover that transcriptome-wide mRNA m6A level, K27-Ub intensity on METTL14 and RLIM expression exhibit coordinated periodic oscillations during the cell cycle. Furthermore, this periodic regulation is mediated by CDK1/cyclin B1-directed phosphorylation of RLIM, triggering self-ubiquitination and proteasomal degradation. Functional investigations across multiple models, including human RLIM-knockout cells, myeloid-specific Rlim-knockout mice and participants with acute monocytic leukemia, demonstrate the pathophysiological importance of this previously unrecognized CDK1/cyclin B1-RLIM-METTL14-m6A axis. In summary, our findings identify a cell-cycle-coupled quality control mechanism for epitranscriptomic m6A regulation.