Human Smc5/6 recognizes transcription-generated positive DNA supercoils

Beyond its essential roles in ensuring faithful chromosome segregation and genomic stability, the human Smc5/6 complex acts as an antiviral factor. It binds to and impedes the transcription of extrachromosomal DNA templates; an ability which is lost upon chromosomal DNA integration. How the complex distinguishes among different DNA templates is unknown. Here we show that, in human cells, Smc5/6 preferentially binds to circular rather than linear extrachromosomal DNA. We further show that this binding is unlikely due to differences in the chromatin composition. Instead, the transcriptional process, per se, and more specifically the accumulation of DNA secondary structures known to be substrates for topoisomerases, is responsible for Smc5/6 recruitment. Those findings, in conjunction with our genome-wide Smc5/6 binding analysis showing that Smc5/6 localises at few but highly transcribe chromosome loci, reveal a previously unforeseen role of Smc5/6 in DNA topology management during transcription. Examination of HA-Smc6, RNAP II and GapR-HA whole genome binding/occupancy (ChIP-Seq) in immortalized human retina pigment epithelial cells (hTERT-RPE1).