Circles in action, circles in function

Circular RNAs were identified more than 20 years ago and thought, at the time, to simply represent rare biochemical curiosities, indicative of an “error-prone” splicing machinery (1-3). It was not until recently, with the advent of next generation sequencing, that such non-linear transcripts were found to be ubiquitously expressed and in certain cases being more abundant that the corresponding linear transcripts (4). Moreover, functional properties have started to be assigned to these molecules, including binding to proteins and acting as miRNAs traps (5,6). In their recent work Yu et al provide convincing evidence for the functionality of a circular RNA from the SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily A, member 5 (SMARCA5) locus, cSMARCA5, containing exons 15 and 16 of the SMARCA5 gene back-spliced together (7).