Transcriptional activator that regulates the tissue specific expression of multiple genes, especially in pancreatic islet cells and in liver (By similarity). Binds to the inverted palindrome 5'- GTTAATNATTAAC-3' (PubMed:10966642, PubMed:12453420). Activates the transcription of CYP1A2, CYP2E1 and CYP3A11 (By similarity). {ECO:0000250|UniProtKB:P22361, ECO:0000269|PubMed:10966642, ECO:0000269|PubMed:12453420}. (Microbial infection) Plays a crucial role for hepatitis B virus gene transcription and DNA replication. Mechanistically, synergistically cooperates with NR5A2 to up-regulate the activity of one of the critical cis-elements in the hepatitis B virus genome enhancer II (ENII). {ECO:0000269|PubMed:14728801, ECO:0000269|PubMed:38018242}. This is the function of ENSG00000135100 (HNF1A, HNF1 homeobox A).