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 (PubMed:17699751, PubMed:19732766). May be a transcriptional regulator. Acts as a positive regulator of HIVEP1 which specifically binds to the DNA sequence 5'-GGGACTTTCC-3' found in enhancer elements of numerous viral promoters such as those of HIV-1, SV40, or CMV (PubMed:19732766). Interacts with HIVEP1 (PubMed:19732766) Interacts with NOL11 (PubMed:22916032). Interacts directly with UTP15 and WDR43 (PubMed:24219289). 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 (PubMed:17699751, PubMed:22916032). Found predominantly at the fibrillar center. May be phosphorylated during mitosis; may control the association of this protein with WRD43 and UTP15. May be due to intron retention. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus. Extended N-terminus.