Regulatory RNAs discovered in unexpected places

Recent studies have discovered both small and long noncoding RNAs (ncRNAs) encoded in unexpected places. These ncRNA genes were surprises at the time of their discovery, but many quickly became well-accepted families of functional regulatory RNA species. Even after years of extensive gene annotation studies using high-throughput sequencing technologies, new types of ncRNA genes continue to be discovered in unexpected places. We highlight ncRNAs that have atypical structures and that are encoded in what are generally considered 'junk' sequences, such as spacers and introns. We also discuss current bottlenecks in the approaches for identifying novel ncRNAs and the possibility that many remain to be discovered.