Positive brassinosteroid-signaling protein. Mediates downstream brassinosteroid-regulated growth response and feedback inhibition of brassinosteroid (BR) biosynthetic genes (PubMed:17699623, PubMed:19220793). May act as transcriptional repressor by binding the brassinosteroid-response element (BREE) (5'-CGTG(T/C)G-3') in the promoter of DLT (AC Q9LWU9), another positive regulator of BR signaling (PubMed:19220793). Acts as transcriptional repressor of LIC, a negative regulator of BR signaling, by binding to the BRRE element of its promoter. BZR1 and LIC play opposite roles in BR signaling and regulation of leaf bending (PubMed:22570626). Interacts with GF14C (PubMed:17699623). Interacts with PUB24 (PubMed:30920691). Interacts with SMOS1 (PubMed:28100707). Brassinosteroid promotes nuclear localization, and binding to GF14C is required for cytoplasmic retention and efficient inhibition of BZR1 when brassinosteroid levels are low. Down-regulated by 24-epibrassinolide. Phosphorylated on serine and threonine residues by GSK2 (PubMed:22685166). Dephosphorylated during response to brassinosteroid (PubMed:17699623, PubMed:22685166). Ubiquitinated by PUB24 (PubMed:30920691). Ubiquitination leads to its subsequent degradation by the 26S proteasome, thus reducing sensitivity to brassinosteroid signaling (PubMed:30920691). Plants silencing BZR1 are dwarf with erect leaves, and have reduced brassinosteroid sensitivity and altered expression of brassinosteroid-responsive genes. Belongs to the BZR/LAT61 family. Extended N-terminus.