Bms1 is an essential, evolutionarily conserved, nucleolar protein. Its depletion interferes with processing of the 35S pre-rRNA at sites A0, A1, and A2, and the formation of 40S subunits. Bms1, the putative endonuclease Rc11, and the essential U3 small nucleolar RNA form a stable subcomplex that is believed to control an early step in the formation of the 40S subunit []. The N terminus of Bms1 contains a guanine nucleotide-binding (G) domain that functions intramolecularly. It is believed that Rc11 activates Bms1 by acting as a guanine-nucleotide exchange factor (GEF) to promote GDP/GTP exchange, and that activated (GTP-bound) Bms1 delivers Rc11 to the preribosomes [].This entry represents the N-terminal domain of Bms1.
This domain is found at the C terminus of the ribosome biogenesis protein BMS1 and TSR1 families, which may act as a molecular switch during maturation of the 40S ribosomal subunit in the nucleolus.
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 [, , ].This entry represents a domain found in Bms1 and Tsr1, and includes cases, such as Tsr1, where it may not function as a guanine nucleotide-binding domain.
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 [, , ].
