Dim2p, a KH-domain protein required for small ribosomal subunit synthesis

Abstract

Recent proteomic analyses are revealing the dynamics of preribosome assembly. Following cleavage at processing site A 2 , which generates the 20S pre-rRNA (the immediate precursor to the 18S rRNA), early RRPs (ribosomal RNA processing factors) are released in bulk from the preribosomes, and the resulting pre-40S subunits are left associated with a limited set of proteins that we refer to as the SSU RRP complex. Dim2p, a core constituent of the SSU RRP complex and conserved KH-domain containing protein, is required for pre-rRNA processing and is associated with early nucleolar and late cytoplasmic pre-rRNA species. Consistently, Dim2p shuttles between the nucle(ol)us and the cytoplasm, a trafficking that is tightly regulated by growth. The association of Dim2p with the 18S rRNA dimethyltransferase Dim1p, as well as its requirement for pre-rRNA processing at cleavage sites A 1 and A 2 and for 18S rRNA dimethylation, suggest that Dim2p may recruit Dim1p to nucleolar pre-rRNAs through its KH domain.

PIN domain of Nob1p is required for D-site cleavage in 20S pre-rRNA

“…These two proteins, however, have no domains known to be associated with proteasome function, but do have domains associated with RNA metabolism, for example, the PIN domain in Nob1p and the KH-domain in Pno1p (Peng et al 2003;Senapin et al 2003;Vanrobays et al 2004). In light of our earlier work (Fatica et al 2003a) and the data presented here, it seems clear that both Nob1p and Pno1p (also called Rrp20p or Dim2p) have primary functions in ribosome synthesis.…”

TOR regulates the subcellular distribution of DIM2, a KH domain protein required for cotranscriptional ribosome assembly and pre-40S ribosome export

“…1A-C; Senapin et al 2003;Vanrobays et al 2004). Detailed blast analysis and homology modeling indicated that the KH domain of DIM2 is of type I, corresponding to a motif of about 70 amino acid residues in length that exhibits the canonical b1-a1-a2-b2-b3-a3 fold and the invariant GXXG central loop sequence (Grishin 2001).…”

“…2A, cf. lanes 1-3 and 7-15; Vanrobays et al 2004). The G207A mutation was sufficient to inhibit pre-rRNA processing at sites A 1 and A 2 , leading to a strong accumulation of the 22S RNA; however, in this case, and in agreement with the partial growth restoration, there was a persistent though reduced production of 20S and 27SA 2 pre-rRNAs and 18S rRNA ( Fig.…”

“…Strikingly, many ribosome synthesis factors are nucleocytoplasmic shuttling proteins that engage the assembly pathway at early nucleolar stages, escort pre-ribosomes along their maturation course through the nucleoplasm, the nuclear pore complexes (NPC), and into the cytoplasm. The KH-domain containing protein DIM2 (YOR145C) is one such trans-acting factor and, as known, functions in the nucleolus and the cytoplasm (Senapin et al 2003;Vanrobays et al 2004). Indeed, DIM2 is required for early nucleolar pre-rRNA processing and late cytoplasmic pre-rRNA methylation and is associated with nascent transcripts and cytoplasmic pre-rRNAs.…”

“…The synthesis of ribosomal components in equimolar amounts entails extensive coordination and integration and is under the tight control of regulatory cascades such as the target of rapamycin (TOR), which provides nutrient-related growth control (for reviews, see Jorgensen et al 2004;Loewith and Hall 2004). The nucleo-cytoplasmic shuttling of DIM2 is tightly regulated by growth (Vanrobays et al 2004), but what triggers its dynamic subcellular trafficking is currently not known.…”