LFB1 HNF1 ACTS AS A REPRESSOR OF ITS OWN TRANSCRIPTION/

LFB1/HNF1 is a hepatocyte-enriched trans-activator involved in the reg ulation of many liver-specific genes. We report the cloning and charac terization of a rat genomic DNA fragment containing about 3.5 kb of th e LFB1/HNF1 gene 5'-flanking region. This DNA segment is capable of di recting the liver-specific expression of a reporter gene in transfecti on assays. More interestingly, the basal activity of the LFB1/HNF1 pro moter in cultured hepatoma cell lines is downregulated by exogenously added LFB1/HNF1 protein itself. The ability to repress transcription s tarting from its own promoter requires the integrity of the N-terminal LFB1/HNF1 DNA-binding domain. Contrary to the expectations, in vitro binding experiments failed to demonstrate any specific and functional interaction of purified LFB1/HNF1 with the -3.5 kb promoter sequence. In addition to the DNA-binding domain, a 60 aa region contained in the C-terminus of the protein and distinct from the previously characteri zed activation domains, is also required for the repressing function.