Arsenic-induced transcriptional interference generates arm-wide ?H2A, with distinct telomeric and centromeric responses

Arsenic is a widespread environmental carcinogen, yet how exposure promotes tumorigenesis remains unclear. Prevailing models attribute arsenic genotoxicity to reactive oxygen species and replication-associated DNA breaks. Using calibrated ?H2A mapping and genetics in budding yeast, we show that As(III) rapidly elicits a diffuse, chromosome-arm-spanning ?H2A response that is replication-independent and occurs without oxidative stress. Instead, arsenic reduces RNA polymerase II chromatin occupancy and promotes loss of the Rpb1 subunit, consistent with acute transcriptional interference. We propose that transcription stress generates transient ssDNA intermediates that activate DNA damage signaling and require homologous recombination (HR) for resolution. Notably, the response is domain-specific: As(III) dampens subtelomeric ?H2A while increasing telomere-proximal HR, and it promotes HR-factor recruitment together with Pol e accumulation at centromeres. In human cells, short-term As(III) activates ATR and induces RPA foci and ?H2AX. Together, these findings shift the early trigger of arsenic genotoxicity from ROS-driven breaks to transcription-linked ssDNA signaling. Overall design: ChIP–seq profiling of S129-phosphorylated histone H2A (?H2A) in wild-type Saccharomyces cerevisiae cells in log phase or arrested in G1 and G2/M, in the presence or absence of As(III). ChIP–seq profiling of S129-phosphorylated histone H2A (?H2A) in log-phase wild-type Saccharomyces cerevisiae cells in the presence or absence of phleomycin. ChIP–seq profiling of S129-phosphorylated histone H2A (?H2A) in log-phase H2A S129A mutant Saccharomyces cerevisiae cells in the presence or absence of As(III). ChIP–seq profiling of S129-phosphorylated histone H2A (?H2A) in G1-arrested Saccharomyces cerevisiae cells lacking KU70 in the presence or absence of As(III). ChIP–seq profiling of S129-phosphorylated histone H2A (?H2A) in log-phase rpb1-1 Saccharomyces cerevisiae cells grown at 25°C or shifted to 37°C. ChIP–seq profiling of Tel1-12Pk in wild-type log-phase Saccharomyces cerevisiae cells in the presence or absence of As(III). ChIP–seq profiling of RPA in wild-type log-phase Saccharomyces cerevisiae cells in the presence or absence of As(III). ChIP–seq profiling of Rad52-YFP in wild-type log-phase Saccharomyces cerevisiae cells in the presence or absence of As(III). ChIP–seq profiling of Rad51 in wild-type log-phase Saccharomyces cerevisiae cells in the presence or absence of As(III). ChIP–seq profiling of Rad59-13cMyc in wild-type log-phase Saccharomyces cerevisiae cells in the presence or absence of As(III). ChIP–seq profiling of Rpb1 in wild-type log-phase Saccharomyces cerevisiae cells in the presence or absence of As(III). ChIP–seq profiling of Rap1-13cMyc in G2/M-arrested wild type Saccharomyces cerevisiae cells in the presence or absence of As(III). ChIP–seq profiling of Cdc13-18cMyc in G2/M-arrested wild type Saccharomyces cerevisiae cells in the presence or absence of As(III). ChIP–seq profiling of Pol2-3HA in wild-type log-phase Saccharomyces cerevisiae cells in the presence or absence of As(III).