Required for the early cleavages at sites A0, A1 and A2 during 18S ribosomal pre-RNA processing. Component of a heterotrimeric complex containing IMP3, IMP4 and MPP10. Interacts with MPP10. Component of the ribosomal small subunit (SSU) processome composed of at least 40 protein subunits and snoRNA U3. Belongs to the universal ribosomal protein uS4 family.