Live-cell single-molecule dynamics of eukaryotic RNA polymerase machineries

Eukaryotic gene expression in the nucleus is orchestrated by three RNA polymerases (RNAP-I, -II, and -III) and associated factors ^1,2 . Despite extensive biochemical, genomic, structural, and imaging studies, the real-time dynamics of these transcription complexes remain obscure. Here, we employ single-molecule tracking in living yeast to assess the physiological kinetics of over 50 representative proteins encompassing all three RNAP machineries. Components of RNAPI and RNAPIII pre-initiation complexes (PICs) engage in long-lived interactions on chromatin, reflecting their roles for constitutive rRNA and tRNA synthesis, in contrast to the transient RNAPII PIC. We further report the dynamics of key components across the RNAPII transcription cycle ^2–5 —factors for upstream regulation, elongation, histone modification, RNAPII C-terminal domain (CTD) modification, RNA processing, and termination—revealing unprecedented insights into the temporal landscape of RNAPII transcription. Strikingly, many elongation factors, previously thought to travel processively with RNAPII, display transient residence times, suggesting highly dynamic interactions rather than constant association. Systematic screening of RNAPII-associated factors shows that truncation of RNAPII-CTD substantially reduces U1 snRNP residence time and decreases intron retention in ribosomal protein genes, providing insights into how CTD length influences co-transcriptional splicing. Our findings establish a framework for dynamic chromatin interactions of RNA polymerase machineries in living cells.