"Thought to result from splicing errors, circular RNA species possess no known function." Source RNA Journal 2013.

RNA usually occurs in strands, but can also form circular loops. It's predominantly found in a cell's cytoplasm - i.e. outside the cell nucleus.

It's now known that Circular RNA (circRNA) can code for protein production, but in general its functions are still largely unknown.

Many geneticists currently tend to regard circRNA as functional rather than accidental. Several theories have been put forward to explain possible functions - including as a 'sponge' to 'soak up' genetic errors during cell divisions. (See Wikipedia)

At its core, circRNA is a single stranded RNA, but it differs from the far better known linear RNA in that it continuously closed in on itself by covalently joining its 5′ and 3′ ends, thus presenting some fascinating properties which are not fully explored: protein complex scaffolding, parental gene modulation, RNA-protein interactions and microRNA (miRNA) sponge, just to name a few.

Source : ExRNA 2, 1 (2020)

Also see DNA / RNAplugin-autotooltip__plain plugin-autotooltip_bigDNA / RNA

The vast majority of human DNA lies outside of the genes within the cells. Of this, recent work has discovered that 85% of these stretches of DNA appear to make RNA - which, for the most part, have yet-to-be-determined functions.

A study published in the online journal