Ribosome biogenesis factor that coordinates hyperactive transcription and ribogenesis (PubMed:17699751). Part of the small subunit (SSU) processome, first precursor of the small eukaryotic ribosomal subunit. During the assembly of the SSU processome in the nucleolus, many ribosome biogenesis factors, an RNA chaperone and ribosomal proteins associate with the nascent pre-rRNA and work in concert to generate RNA folding, modifications, rearrangements and cleavage as well as targeted degradation of pre-ribosomal RNA by the RNA exosome. Involved in nucleolar processing of pre-18S ribosomal RNA. Required for optimal pre-ribosomal RNA transcription by RNA polymerase I (PubMed:17699751, PubMed:34516797). Essential for stem cell pluripotency and embryonic development. In the nucleoplasm, recruited by promoter-associated/nascent transcripts and transcription to active promoters where it facilitates releases of elongation factor P-TEFb and paused RNA polymerase II to allow transcription elongation and maintain high-level expression of its targets genes (By similarity). {ECO:0000250|UniProtKB:Q6ZQL4, ECO:0000269|PubMed:17699751, ECO:0000269|PubMed:34516797}. This is the function of Ensembl gene identifier ENSG00000163811 (WDR43, WD repeat domain 43).