Extended Data Fig. 10: Nuclear eIF1 regulates nuclear-encoded mitochondrial mRNAs and CDC20.

a, Gene set enrichment analysis using change in translational efficiency between mitotically arrested and interphase cells. Mitochondrial mRNAs are preferentially translated during mitosis. b, Scatterplot comparing translational efficiency of mRNAs during interphase and mitosis. Mitochondrial mRNAs, encoded from both the mitochondria (brown) and nucleus (green), are preferentially translated during mitosis. Removal of nuclear eIF1 is predicted to suppress changes to mitotic translation. c-e, Quantification of 5’UTR luciferase reporters showing the change in translation between interphase and mitosis for the indicated reporter in cells with or without nuclear eIF1. n = 4 biological replicates and paired T-test was used. We note that the mechanism by which eIF1 affects the translation of mitochondrial mRNAs remains unclear. f, Positive control experiment to show that TMRE is staining active mitochondria. Addition of cyanide poisons the electron transport chain, resulting in mitochondrial depolarization. TMRE signal is quantified using Cell Profiler. g, Median TMRE signal in 3 biological replicates. Error bar represents standard error of the mean and unpaired Student’s t-tests was used. h, Mitotic death/slippage assays as described in Fig. 5f, except using an additional monoclonal line or polyclonal lines. n = 3 biological replicates and unpaired T-test was used. i, Schematic outline of the regulation and function alternative CDC20 isoforms³⁸. Leaky ribosome scanning allows for translation of CDC20 from Met43. The short CDC20 isoform bypasses control of the mitotic check point complex to promote mitotic slippage. j, Luciferase mRNA reporter assays to assess the relative translation of CDC20 M1 and M43 translation initiation sites in interphase and mitotically arrested cells. CDC20 M43 reporter is preferentially translated relative to CDC20 M1 reporter in mitosis, consistent with nuclear eIF1 release promoting leaky scanning in mitosis. Error bar represents standard error of the mean, n = 3 biological replicates, and unpaired Student’s t-tests used for this data. k, Ectopic expression of CDC20 M43 isoform rescues slippage/death phenotype observed in cells lacking nuclear eIF1. Mitotic death/slippage assays as described in Fig. 5f. CDC20 M43 transgene was induced with doxycycline 24 h prior to taxol addition and live imaging. Error bars represent standard error of the mean, n = 3 biological replicates, and Unpaired Student’s t-tests was used.

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