Gene architecture is a determinant of the transcriptional response to bulky DNA damages.

Bulky DNA damages block transcription and compromise genome integrity and function. The cellular response to these damages includes global transcription shutdown. Still, active transcription is necessary for transcription-coupled repair and for induction of damage-response genes. To uncover common features of a general bulky DNA damage response, and to identify response-related transcripts that are expressed despite damage, we performed a systematic RNA-seq study comparing the transcriptional response to three independent damage-inducing agents: UV, the chemotherapy cisplatin, and benzo[a]pyrene, a component of cigarette smoke. Reduction in gene expression after damage was associated with higher damage rates, longer gene length, and low GC content. We identified genes with relatively higher expression after all three damage treatments, including NR4A2, a potential novel damage-response transcription factor. Up-regulated genes exhibit higher exon content that is associated with preferential repair, which could enable rapid damage removal and transcription restoration. The attenuated response to BPDE highlights that not all bulky damages elicit the same response. These findings frame gene architecture as a major determinant of the transcriptional response that is hardwired into the human genome.

Exons and introns exhibit transcriptional strand asymmetry of dinucleotide distribution, damage formation and DNA repair.

Recent cancer sequencing efforts have uncovered asymmetry in DNA damage induced mutagenesis between the transcribed and non-transcribed strands of genes. Here, we investigate the major type of damage induced by ultraviolet (UV) radiation, the cyclobutane pyrimidine dimers (CPDs), which are formed primarily in TT dinucleotides. We reveal that a transcriptional asymmetry already exists at the level of TT dinucleotide frequency and therefore also in CPD damage formation. This asymmetry is conserved in vertebrates and invertebrates and is completely reversed between introns and exons. We show the asymmetry in introns is linked to the transcription process itself, and is also found in enhancer elements. In contrast, the asymmetry in exons is not correlated to transcription, and is associated with codon usage preferences. Reanalysis of nucleotide excision repair, normalizing repair to the underlying TT frequencies, we show repair of CPDs is more efficient in exons compared to introns, contributing to the maintenance and integrity of coding regions. Our results highlight the importance of considering the primary sequence of the DNA in determining DNA damage sensitivity and mutagenic potential.