InterPro domain: IPR044281

This family represents the U3 small nucleolar ribonucleoprotein protein IMP4 and Ribosome production factor 1 RPF1 that belong to the IMP4 superfamily. This superfamily contains a Brix (biogenesis of ribosomes in Xenopus) domain, a region of 150-180 residues length, and it is characterised by the sigma70-like motif, a sequence motif first identified in the sigma70 family of prokaryotic transcription factors, which is sufficient to confer RNA binding activity [ 1 , 2 , 3 ]. IMP4 is a component of the 60-80S U3 small nucleolar ribonucleoprotein (U3 snoRNP) and it is required for the early cleavages during pre-18S ribosomal RNA processing [ 4 , 4 ]. RPF1 is a essential protein involved in ribosome biogenesis [ 5 ].

1. The human Imp3 and Imp4 proteins form a ternary complex with hMpp10, which only interacts with the U3 snoRNA in 60-80S ribonucleoprotein complexes. Nucleic Acids Res 31, 1877-87
2. The sigma(70)-like motif: a eukaryotic RNA binding domain unique to a superfamily of proteins required for ribosome biogenesis. Mol. Cell 9, 329-39
3. Functional analysis in yeast of the Brix protein superfamily involved in the biogenesis of ribosomes. FEMS Yeast Res. 3, 35-43
4. Imp3p and Imp4p mediate formation of essential U3-precursor rRNA (pre-rRNA) duplexes, possibly to recruit the small subunit processome to the pre-rRNA. Proc Natl Acad Sci U S A 101, 15301-6