Table 6.
Small subunit processome subcomplexes and early assembly factors.
| Yeast | 40S | 60S | Human | 40S | 60S | Function in early nucleolar ribosome biogenesis | Citation |
|---|---|---|---|---|---|---|---|
| Utp4 | x | UTP4/CIRH1A | x | UTP‐A complex, interacts with the start of 5′ ETS, required for recruitment of UTP‐B and U3 snoRNP, essential for formation of 5′ ETS particle | Krogan et al (2004), Prieto and McStay (2007), Freed et al (2012), Chaker‐Margot et al (2017) and Singh et al (2021) | ||
| Utp5 | x | UTP5/WDR43 | x | ||||
| Utp8 | x | NOL11 | x | ||||
| Utp9 | x | ||||||
| Utp10 | x | UTP10/HEATR1 | x | ||||
| Utp15 | x | UTP15 | x | ||||
| Utp17 | x | UTP17/WDR75 | x | ||||
| Pol5 | x | x | MYBBP1A | x | |||
| Utp1/Pwp2 | x | PWP2 | x | UTP‐B complex, binds 5′ ETS and U3 snoRNA, supports structural pre‐rRNA remodeling, essential for formation of 5′ ETS particle, Utp18 contains exosome interaction motif | Krogan et al (2004), Sloan et al (2015), Barandun et al (2017), Barandun et al (2018) and Singh et al (2021) | ||
| Utp6 | x | UTP6 | x | ||||
| Utp12/Dip2 | x | UTP12/WDR3 | x | ||||
| Utp13 | x | TBL3 | x | ||||
| Utp18 | x | UTP18 | x | ||||
| Utp21 | x | WDR36 | x | ||||
| DDX21 | x | ||||||
| NOP2 | x | ||||||
| Nop1 | x | FBL | x | U3 snoRNP, U3 snoRNA base pairs with 5′ ETS, chaperones pre‐rRNA folding steps, essential for formation of 5′ ETS particle | Kiss‐László et al (1996), Grandi et al (2002), Barandun et al (2017) and Singh et al (2021) | ||
| Nop56 | x | NOP56 | x | ||||
| Nop58 | x | NOP58 | x | ||||
| Snu13 | x | SNU13/15.5 K | x | ||||
| Rrp9 | x | U3‐55K/U3IP2 | x | ||||
| Mpp10 | x | MPHOSPH10 | x | Mpp10‐Imp3‐Imp4 complex, interacts with U3 snoRNA, supports formation of 5′ ETS particle | Lee and Baserga (1999) and Granneman et al (2003) | ||
| Imp3 | x | IMP3 | x | ||||
| Imp4 | x | IMP4 | x | ||||
| Rrp7 | x | RRP7A | x | UTP‐C complex, chaperones 5′ domain of 18S rRNA | Baudin‐Baillieu et al (1997), Krogan et al (2004), Rudra et al (2007), Barandun et al (2017) and Singh et al (2021) | ||
| Utp22 | x | NOL6 | x | ||||
| Cka1 | x | CK2A1 | x | ||||
| Cka2 | x | CK2A2 | x | ||||
| Ckb1 | x | CK2N | x | ||||
| Ckb2 | x | CK2N | x | ||||
| Rrp36 | x | RRP36 | x | ||||
| Utp7 | x | WDR46 | x | Sof1‐Utp7 complex, aids organization of A1 cleavage site | Barandun et al (2017) | ||
| Utp14 | x | UTP14A | x | ||||
| Sof1 | x | WDSOF1 | x | ||||
| Rcl1 | x | RCL1 | x | Rcl1‐Bms1‐complex, GTPase activity (Bms1), mediates cleavage at A2 site, also required for A0 and A1 cleavage, interacts with U3 snoRNP | Karbstein and Doudna (2006) and Horn et al (2011) | ||
| Bms1 | x | BMS1 | x | ||||
| Enp1 | x | ENP1/BYSL | x | In yeast: Nop14‐Noc4‐Enp1 complex, in humans: NOP14‐NOC4L‐UTP14A‐EMG1, structural role: binds to 3′ domain of 18S pre‐RNA, Emg1: methyltransferase | Liu and Thiele (2001), Kühn et al (2009), Warda et al (2016) and Barandun et al (2017) | ||
| Utp2/Nop14 | x | NOP14 | x | ||||
| Noc4 | x | NOC4L | x | ||||
| Emg1 | x | EMG1 | x | ||||
| Bfr2 | x | AATF | x | in humans: ANN complex, required for cleavage at A0, 1 and in the ITS1, in yeast: Bfr2‐Enp2 recruit Dpb4 | Soltanieh et al (2014) and Bammert et al (2016) | ||
| Lcp5 | x | NGDN | x | ||||
| Enp2 | x | NOL10 | x | ||||
| XRN2 | x | XND complex, required for A′ cleavage, recruits XRN2 for degradation of excised spacer fragment | Dragon et al (2002) and Memet et al (2017) | ||||
| NKRF | x | ||||||
| Prp43 | DHX15 | x | |||||
| Utp30 | x | RSL1D1 | x | Utp30‐Rrt14 complex, binds 5′ ETS and pre‐18S rRNA, Rrt14 is non‐essential | Barandun et al (2017) | ||
| Rrt14 | x | ||||||
| Utp11 | x | UTP11 | x | ||||
| Bud21/Utp16 | x | NOL7 | x | Required for 18S pre‐rRNA processing | Dragon et al (2002) and Singh et al (2021) | ||
| Fcf2 | x | TDIF2 | x | Binds U3 snoRNP, TDIF2 contains AIM putative motif | Rempola et al (2006), Barandun et al (2017) and Singh et al (2021) | ||
| Sas10 | x | UTP3 | x | Stabilizes and chaperones Mpp10 complex to nucleolus, blocks Emg1 active site | Zhao et al (2019) | ||
| Utp24 | x | UTP24 | x | Endoribonuclease, couples pre‐rRNA cleavages in yeast at sites A1 and A2, in humans: site 1 and E | Bleichert et al (2006) and Wells et al (2016) | ||
| Esf1 | x | ESF1 | Involved in early pre‐rRNA processing | Peng et al (2004) | |||
| Esf2 | x | ABT1 | Stimulates Dbp8 | Granneman et al (2006b) | |||
| Dbp8 | x | DDX49 | x | DEAD box RNA helicase | Granneman et al (2006b) and Awasthi et al (2018) | ||
| Dbp4 | x | DDX10 | x | DEAD box RNA helicase | Granneman et al (2006a) and Turner et al (2009) | ||
| Rrp3 | x | DDX47 | x | DEAD box RNA helicase | Granneman et al (2006a) | ||
| Bud22 | x | SRFBP1 | Dakshinamurthy et al (2010) | ||||
| Efg1 | x | Required for 18S pre‐rRNA processing (A1, A2), initiates degradation of aberrant 23S pre‐rRNA | Choque et al (2018) | ||||
| Rrp5 | x | x | PDCD11 | x | x | Structural SSU component supporting pre‐rRNA, compaction, important for 18S maturation (site A0‐A2) and 5.8S processing (site A3) | Venema and Tollervey (1996) and Lebaron et al (2013) |
| Krr1 | x | KRR1 | x | Interacts with Faf1, important for 40S platform, assembly as it is replaced by Dim2 | Zheng et al (2014) and Sturm et al (2017) | ||
| Rok1 | x | DDX52 | x | DEAD box RNA helicase, releases Rrp5, releases snR30 | Khoshnevis et al (2016) | ||
| Utp25 | x | DEF/C1orf107 | x | Charette and Baserga (2010) and Tao et al (2017) | |||
| Kri1 | x | KRI1 | Interacts with Krr1 | Sasaki et al (2000) | |||
| Utp23 | x | UTP23 | x | Endoribonuclease, in yeast: likely inactive, in humans: cleavage at site A0 | Wells et al (2017) | ||
| Fyv7 | x | Peng et al (2003) | |||||
| Mrd1 | x | RBM19 | x | Aids formation of central pseudoknot, required for dynamic U3 snoRNA‐rRNA interaction (release) | Segerstolpe et al (2013) and Lackmann et al (2018) | ||
| Fal1 | x | DDX48/EIF4A3 | x | DEAD box RNA helicase | Kressler et al (1997) and Davila Gallesio et al (2020) | ||
| Sgd1 | x | NOM1 | x | Fal1 cofactor | Davila Gallesio et al (2020) | ||
| Cms1 | x | CMS1 | x | Grandi et al (2002) | |||
| Nop9 | x | NOP9 | Impedes Nob1 cleavage | García‐Gómez et al (2011) and Zhang et al (2016a) | |||
| Nop6 | x | Not essential for ribosome biogenesis | García‐Gómez et al (2011) | ||||
| Utp20 | x | UTP20 | x | Associates with faulty intermediates, might play a role in rRNA quality control | Dez et al (2007) | ||
| Kre33 | x | NAT10 | x | ATP‐dependent RNA acetyltransferase | Ito et al (2014) and Sharma et al (2017, 2015) | ||
| Faf1 | x | C1orf131 | Interacts with Krr1/KRR1 | Zheng et al (2014) and Singh et al (2021) | |||
| Dim2/Pno1 | x | PNO1/DIM2 | x | Interacts with Nob1 | Chaker‐Margot et al (2017) | ||
| Rrp12 | x | RRP12 | x | Part of the 3′ minor domain | Ameismeier et al (2018) | ||
| Nob1 | x | NOB1 | x | Endoribonuclease, associates with ITS1, catalyzes removal of final part of ITS1 (site D/3), might only associate in nucleoplasm | Fatica et al (2004) | ||
| Dhr1 | x | DHX37 | x | DEAH box RNA helicase, releases U3 snoRNA | Boneberg et al (2019) | ||
| Dhr2 | x | DEAH box RNA helicase, interacts with Utp25 and Nop19 | Granneman et al (2006a) | ||||
| Nop19 | x | Important for Utp25 incorporation | Choque et al (2011) | ||||
| Rrp8 | x | NML/RRP8 | x | Methyltransferase | Peifer et al (2013) | ||
| Slx9 | x | FAM207A/C21orf70 | Non‐essential, supports efficient ITS1 processing | Bax et al (2006) | |||
| Pol5 | x | x | MYBBP1A | x | Turnover of 5′ ETS fragment, required for recycling of SSU RBFs | Braun et al (2020) | |
| Bud23 | x | WBSCR22 | x | Methyltransferase, supports disassembly of SSU particle | Black et al (2020) | ||
| Nip7 | x | NIP7 | x | In contrast to yeast, human NIP7 and FTSJ3 were shown to function in 40S biogenesis | Morello et al (2011a) | ||
| Sbp1 | x | FTSJ3 | x |