Transcription factor involved in RNA polymerase II (RNAPII) transcription regulation. Involved in transcription elongation. May function at post-recruitment and elongation steps of transcription. May be recruited by BZR2/BES1 to target genes and promote their expression during transcription elongation process. Required for brassinosteroid (BR)-induced gene expression (PubMed:20139304). Required the for regulation of numerous nitrogen-responsive genes in roots. Acts in roots to repress NRT2.1 transcription in response to high nitrogen supply. This repression is associated with an IWS1-dependent increase of trimethylation on 'Lys-27' H3K27me3 at the NRT2.1 locus (PubMed:21788519). Interacts with BZR2/BES1 and SPT6 (via N-terminus) (PubMed:20139304). Interacts with ASHH2/SDG8 (PubMed:24838002). A number of isoforms are produced. According to EST sequences. Semi-dwarf phenotype. Stunted growth characterized by reduced leaf petiole lengths and small leaves. Altered responses to brassinosteroid (BR). Belongs to the IWS1 family.