InterPro domain: IPR039761

Bms1p and Tsr1p represent a new family of factors required for ribosomebiogenesis. They are each independently required for 40S ribosomal subunitbiogenesis. Bms1p, a protein required for pre-rRNA processing, contains anevolutionarily conserved guanine nucleotide-binding (G) domain with five conserved polypeptide loopsdesignated G1 through G5, which form contact sites with the guanine nucleotideor coordinate the Mg(2+) ion. Sequences resembling G1 (consensus [GA]-x(4)-G-K-[ST]; also known as a P-loop), G4 (consensus [NT]-K-x-D), and G5 (consensusS-[AG] are present in all Bms1 proteins, and either fully conform with theconsensus or contain, at most, single conservative substitutions. The G2 motif(consensus G-P-[IV]-T) contains a T residue involved in the coordination ofthe Mg(2+) required for GTP hydrolysis. The G3 motif diverges from theconsensus found in G proteins, D-x(2)-G; however, the D residue is replacedwith the conserved E residue. In contrast, Tsr1p lacks a P-loop and is notpredicted to bind GTP. It functions at a later step of 40S ribosomeproduction, possibly in assembly and/or export of 43S pre-ribosomal subunitsto the cytosol [ 1 , 2 , 3 ].

1. Classification and evolution of P-loop GTPases and related ATPases. J. Mol. Biol. 317, 41-72
2. Bms1p, a G-domain-containing protein, associates with Rcl1p and is required for 18S rRNA biogenesis in yeast. RNA 7, 1254-67
3. Bms1p, a novel GTP-binding protein, and the related Tsr1p are required for distinct steps of 40S ribosome biogenesis in yeast. RNA 7, 1268-83