Table 1.

RNA helicases in ribosome biogenesis and their presumed functions

Name	Type	Maturation step	Cofactors	Known or hypothesized function in RNA folding/unwinding
Fal1	DEAD	90S	Sgd1	unknown
Dbp8	DEAD	90S	Esf2	unknown
Dbp4/Hca4	DEAD	90S	unknown	18S rRNA 5’ domain folding; U14 release
Rrp3	DEAD	90S	unknown	unknown
Rok1	DEAD	90S	Rrp5	snR30 release from 90S particles; Rrp5 release from 90S particles
Dhr2	DEAH	90S, (early pre-40S)	unknown	unknown
Dhr1/Ecm16	DEAH	90S, early pre-40S	Utp14	promotion of A1 cleavage; release of the U3 snoRNA from the 18S rRNA, which triggers formation of the central pseudoknot
Prp43	DEAH	90S, pre-40S, pre-60S	Pfa1, Pxr1 (G-patch)	snoRNA (snR72, snR60, others) release; 18S rRNA H44 restructuring
Has1	DEAD	90S, early to late nucleolar pre-60S	unknown	U14 release; Rrp36 release; contact formation between 25S rRNA domain I and 5.8S rRNA
Mtr4	Ski2-like	90S, nucleoplasmic pre-60S	unknown	5’ETS and ITS2 unwinding and recruitment of the nuclear exosome for 3’-5’ degradation of these spacer elements
Dbp6	DEAD	(90S), early nucleolar pre-60S	unknown	unknown
Dbp7	DExD	(90S), early nucleolar pre-60S	unknown	snR190 (possibly also snR34) release
Dbp9	DEAD	early nucleolar pre-60S	unknown	unknown
Dbp3	DEAD	early nucleolar pre-60S	unknown	snoRNA release; ITS1 re-arrangement
Drs1	DEAD	early/intermediate nucleolar pre-60S	unknown	promotion of A2 cleavage; stable Nop7–Erb1–Ytm1 incorporation
Mak5	DEAD	early/intermediate nucleolar pre-60S	unknown	25S rRNA H39 restructuring
Dbp2	DEAD	early/intermediate nucleolar pre-60S	unknown	U8 snoRNA release in higher eukaryotes; re-arrangement of ITS2 hairpin in yeast; both are proposed to regulate formation of the proximal 25S(28S)/5.8S stem
Dbp10	DEAD	intermediate nucleolar pre-60S	unknown	25S rRNA H89-H92 (PTC) folding
Spb4	DEAD	late nucleolar pre-60S	unknown	25S rRNA H62/H63 restructuring