Involved in nucleolar processing of pre-18S ribosomal RNA. Required for optimal pre-ribosomal RNA transcription by RNA polymerase I together with a subset of U3 proteins required for transcription (t-UTPs). Interacts with snoRNA U3. Interacts with MPP10. Component of the ribosomal small subunit (SSU) processome composed of at least 40 protein subunits and snoRNA U3. In the absence of snoRNA3, forms a complex with other t-UTPs. This complex can associate with pre-18S ribosomal RNAs. Present with 5440 molecules/cell in log phase SD medium.