Dual function regulator of gene expression; regulator of transcription and modulator of alternative splicing. General coactivator of nuclear receptor-induced gene expression, including genes activated by the glucocorticoid receptor NR3C1. Binds to a subset of pre-mRNAs and to components of the spliceosome machinery to directly modulate basal alternative splicing; involved in simple and complex cassette exon splicing events. Binds its own pre-mRNA and regulates its alternative splicing and degradation; one of the alternatively spliced products is a stable intronic sequence RNA (sisRNA) that binds the protein to regulate its ability to affect splicing. Binding of the sisRNA stimulates phase separation and localization to nuclear speckles, which may contribute to activation of nuclear receptor-induced gene expression. May also indirectly modulate alternative splicing. Regulates transcription of genes involved in heart development, neuronal cell function, protein localization and chromatin localization. Regulates splicing of genes involved in neurogenesis and chromatin organization. Essential for central nervous system development. Required for the estrogen-dependent expression of ESR1 target genes. Can act in cooperation with MED1 