Transcription and replication: far relatives make uneasy bedfellows.

Genomes encode all RNAs required for life. For this simple reason the genome's stability is a prerequisite for maintaining the fitness of the cell, the organism and its progeny. Paradoxically, any enzymatic transaction at the DNA, including transcription itself, entails the risk of local destabilization of the DNA helix, thereby threatening genomic integrity. Particularly where transcription and replication meet, the genome may be at an increased risk of nucleotide substitution mutations, deletions or rearrangements. This Extra-view sketches our understanding of the different threats that transcription imposes on genome stability. We will focus on recent work highlighting the role of DNA damage in transcription-associated mutagenesis (TAM) in mammalian cells. Furthermore we discuss the possible implications of TAM for human fitness and disease with an emphasis on carcinogenesis. In addition, we propose an updated nomenclature for the mechanistically different forms of TAM.