Abstract
We report the molecular cloning and the characterization of the Xenopus homolog of mammalian hypoxia‐inducible factor 1α (HIF1α), a member of the bHLH/PAS transcription factor family. Searches in Xenopus genome sequences and phylogenetic analysis reveal the existence of HIF1α and HIF2α paralogs in the Xenopus laevis species. Sequence data analyses indicate that the organization of protein domains in Xenopus HIF1α (xHIF1α) is strongly conserved. We also show that xHIF1α heterodimerizes with the Xenopus Arnt1 protein (xArnt1) with the proteic complex being mediated by the HLH and PAS domains. Subcellular analysis in a Xenopus XTC cell line using chimeric GFP constructs show that over‐expression of xHIF1α and xArnt1 allows us to detect the xHIF1α/xArnt1 complex in the nucleus, but only in the presence of both partners. Further analyses in XTC cell line show that over‐producing xHIF1α and xArnt1 mediates trans‐activation of the hypoxia response element (HRE) reporter. The trans‐activation level can be increased in hypoxia conditions. Interestingly such trans‐activation properties can be also observed when human Arnt1 is used together with the xHIF1α. J. Cell. Biochem. 102: 1542–1552, 2007. © 2007 Wiley‐Liss, Inc.