Bach1 functions as a transcriptional repressor of heme oxygenase-1 (HO-1) and 
the beta-globin genes. The enhancer regions of these genes contain multiple Maf 
recognition elements (MAREs) to which Bach1 can bind. Previous studies have 
shown that increased levels of heme and cadmium induce the nuclear export of 
Bach1, resulting in cytoplasmic accumulation. By means of a yeast two hybrid 
screening using Bach1 as bait, we identified the intracellular hyaluronic acid 
binding protein (IHABP) as a potential regulator of Bach1. IHABP is a 
microtubule-associated protein that may regulate the organization of the 
cytoskeletal network. A series of domain analyses revealed that a region of 
Bach1 previously implicated in cytoplasmic accumulation was necessary for 
IHABP-binding. A C-terminal region of IHABP was necessary for Bach1-binding. 
Overexpressed Bach1 colocalized with IHABP in the cytoplasm, forming fiber-like 
structures on microtubules. Fluorescence recovery after photobleaching (FRAP) 
analysis revealed a dynamic nature of the Bach1-IHABP interaction in living 
cells. The repression of HO-1 reporter activity by Bach1 was attenuated by 
co-transfecting IHABP in a dose-dependent manner. Moreover, the overexpression 
of IHABP induced the endogenous HO-1 gene in NIH3T3 cells. The overall results 
suggest that IHABP regulates the subcelluar localization of Bach1 in order to 
fine-tune transactivation of Bach1 target genes such as HO-1.