Scientists first observed circular RNAs, a type of noncoding RNA, in mammalian cells over 30 years ago but are only now beginning to elucidate their functions. Circular RNAs generally contain either exclusively gene exon or gene intron sequences. Li et al. now describe an unusual class of circular RNAs in human cells that contain both exon and intron sequences. These RNAs localized to the nucleus, where they bound to protein components of the transcription machinery and RNA components of the splicing machinery. By binding to the promoters of their own genes, they fine-tuned transcriptional activation of these genes.
Nat. Struct. Mol. Biol. 10.1038/nsmb.2959 (2015).