Table 1.

Estimation of spatial constraints on RNA processing

Process	Processing substep	Location on pre-mRNA	Minimal distance from processing site (nt)*	Experimental system	Organism	Refs
5′ end capping	NA	5′ end	~20	In vivo	Budding yeast	53, 127
RNA editing	NA	Gene specific	<60	In vivo	Mammals	109
Splicing	Step I	BPS	<40	In vitro	Budding yeast	37
	Step II	3′SS	<40	In vivo	Budding yeast	4
	mRNA release	Splice junction	~20	In vitro	Budding yeast	45
3′ end cleavage	NA	PAS	<200	In vivo	Budding yeast	186, 187

BPS, branchpoint sequence; NA, not applicable; nt, nucleotides; PAS, poly(A) site; SS, splice site.

^*Distances along the pre-mRNA required to start RNA processing. In vivo distance values reflect the amount of transcribed RNA required for the listed processing event; in vitro distance values refer to minimal RNA lengths required by ATPases to trigger these reactions.