Ribosome biogenesis factor. Involved in nucleolar processing of pre-18S ribosomal RNA. Involved in small subunit (SSU) pre-rRNA processing at sites A', A0, 1 and 2b. Required for optimal pre-ribosomal RNA transcription by RNA polymerase. May be a transcriptional regulator. Acts as a positive regulator of HIVEP1. Interacts with HIVEP1. Interacts with NOL11. Interacts directly with UTP15 and WDR43. May be a component of the proposed t-UTP subcomplex of the ribosomal small subunit (SSU) processome containing at least UTP4, WDR43, HEATR1, UTP15, WDR75. Found predominantly at the fibrillar center. Expressed in liver. In 11.5 day embryos, highly and predominantly expressed in liver, with lower expression in somites, brain and craniofacial structures. Expression significantly decreases in 12.5 day embryos and in the newborn. May be phosphorylated during mitosis; may control the association of this protein with WRD43 and UTP15. Truncated N-terminus. Extended N-terminus. Extended N-terminus.