Bits of a gene that don't code for protein can regulate that gene's expression as a loop of RNA.

Ling-Ling Chen, Li Yang and their colleagues at the Shanghai Institutes for Biological Sciences in China examined a class of 'introns' — sequences that reside in the protein-coding portion of genes but get snipped out of the RNA template before the protein is made.

Some introns formed circles that were abundant in the nucleus and, unlike other reported circular RNAs, did not associate with small regulatory RNAs. Reducing levels of the circular intronic RNAs, many of which were unique to human cells, reduced expression of the parent genes.

Mol. Cell http://doi.org/nv6 (2013)