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Nuclear export restricts Gdown1 to a mitotic function

ABSTRACT: Approximately half of purified mammalian RNA polymerase II (Pol II) is associated with a tightly interacting sub-stoichiometric subunit called Gdown1, encoded by the POLR2M gene. Previous in vitro and structural studies have established that Gdown1 potently inhibits transcription initiation through competitive interactions with general transcription factors and blocks the Pol II termination activity of transcription termination factor 2 (TTF2). However, the biological functions of Gdown1 remain poorly understood. Here, we utilized genetic, microscopic, and multi-omics approaches to functionally characterize Gdown1 in multiple human cell lines. Remarkably, acute depletion of Gdown1 led to minimal direct effects on gene expression and transcription. We show that Gdown1 resides predominantly in the cytoplasm of interphase cells, shuttles between the cytoplasm and nucleus, and is directly regulated by nuclear export. Gdown1 enters the nucleus at the onset of mitosis prior to complete breakdown of the nuclear envelope, whereupon association with Pol II becomes possible. Consistently, genetic ablation of Gdown1 is associated with partial de-repression of mitotic transcription, and Gdown1 KO cells present with a growth defect and evidence of aberrant mitoses coupled to p53 pathway activation. Evidence is presented demonstrating that Gdown1 association with Pol II elongation complexes in vitro modulates the combined functions of purified productive elongation factors PAF1C, RTF1, SPT6, DSIF, and P-TEFb. Collectively, our findings support a model wherein the Pol II-regulatory function of Gdown1 occurs during mitosis and is required for genome integrity.

ORGANISM(S): Homo sapiens

PROVIDER: GSE186133 | GEO | 2022/01/03

REPOSITORIES: GEO

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