Nuclear sorting of short RNA polymerase II transcripts.

Mammalian genomes produce an abundance of short RNA. This is, to a large extent, due to the genome-wide and spurious activity of RNA polymerase II (RNAPII). However, it is also because the vast majority of initiating RNAPII, regardless of the transcribed DNA unit, terminates within a ∼3-kb early "pausing zone." Given that the resultant RNAs constitute both functional and non-functional species, their proper sorting is critical. One way to think about such quality control (QC) is that transcripts, from their first emergence, are relentlessly targeted by decay factors, which may only be avoided by engaging protective processing pathways. In a molecular materialization of this concept, recent progress has found that both "destructive" and "productive" RNA effectors assemble at the 5′ end of capped RNA, orchestrated by the essential arsenite resistance protein 2 (ARS2) protein. Based on this principle, we here discuss early QC mechanisms and how these might sort short RNAs to their final fates. [Display omitted] The majority of initiating RNA polymerase II (RNAPII) terminates early, generating an abundance of short RNAs that require sorting into productive or destructive pathways. Here, Garland and Jensen explore early quality-control mechanisms that govern the fate of short RNAs, preventing the accumulation of non-functional transcripts and ensuring proper RNA processing. [ABSTRACT FROM AUTHOR]