City University of Hong Kong. EXTENDED ABSTRACT ONLY- DO NOT CITE

In mammals, hypoxia-inducible factor 1 (HIF-1) is a key transcription factor that controls a variety of cellular and systemic homeostatic responses to hypoxic stress by upregulating the expression of genes involved in enhancing O2 delivery, glucose uptake and glycolysis (Semenza, 2001). HIF-1 is a dimeric basic helix-loop-helix (bHLH) protein composed of HIF-1α and HIF-1β subunits. In vertebrates, the HIF-1α protein and its DNA-binding activity is tightly regulated by O2 concentration and is increased as O2 level decreases (Jiang et al., 1996). So far, two different HIF-α cDNAs have been reported in fish − HIF-1α in Oncorhynchus mykiss (Soitamo et al., 2001) and HIF-2α in Fundulus heteroclitus (Powell and Hahn, 2002). In order to investigate the functional roles of HIF-α in the hypoxia-tolerant grass carp, we have isolated two different full-length HIF-α cDNAs of 3.9 and 2.1 kb from primary kidney cells of grass carp using degenerate RT-PCR and, 5′- and 3′-RACE. Computer analysis indicated that the ORF of the 3.9-kb cDNA encodes for a putative protein of 774 amino acids which shares> 70 % sequenc