IMP4, U3 Small Nucleolar Ribonucleoprotein (IMP4)

IMP4 forms a ternary complex with IMP3 and MPP10 (MPHOSPHO10) that interacts with U3 small nucleolar RNA (snoRNA), which is required for the early cleavage steps in pre-rRNA processing.

The deduced 292-amino acid protein has a calculated molecular mass of 33.7 kD and shares approximately 50% identity with yeast Imp4. IMP4 contains a predicted sigma 70-like motif and a coiled-coil region. Fluorescence microscopy localized IMP4 to the nucleoli in transfected Hep2 cells.Glycerol gradient cosedimentation and GST pull-down studies showed that human IMP4, IMP3, and MPP10 form a heterotrimeric protein complex. Analysis of deletion mutants showed that the IMP4 sigma 70-like motif interacted with the MPP10 region within amino acids 327 to 456.