RNA helicase that acts as a sensor of the transcriptional status of both RNA polymerase(Pol) I and II: promotes ribosomal RNA(rRNA) processing and transcription from polymerase II(Pol II)(PubMed:25470060). Binds various RNAs, such as rRNAs, snoRNAs, 7SK and, at lower extent, mRNAs(PubMed:25470060). In the nucleolus, localizes to rDNA locus, where it directly binds rRNAs and snoRNAs, and promotes rRNA transcription, processing and modification. Required for rRNA 2'-O-methylation, possibly by promoting the recruitment of late-acting snoRNAs SNORD56 and SNORD58 with pre-ribosomal complexes(PubMed:25470060, PubMed:25477391). In the nucleoplasm, binds 7SK RNA and is recruited to the promoters of Pol II-transcribed genes: acts by facilitating the release of P-TEFb from inhibitory 7SK snRNP in a manner that is dependent on its helicase activity, thereby promoting transcription of its target genes(PubMed:25470060). Functions as cofactor for JUN-activated transcription: required for phosphorylation of JUN at 'Ser-77'(PubMed:11823437, PubMed:25260534). Can unwind double-stranded RNA(helicase) and can fold or introduce a secondary structure to a single-stranded RNA(foldase)(PubMed:9461305). Involved in rRNA processing(PubMed:14559904, PubMed:18180292).