Fig. 2. Schematic representation of a newly cloned HIF-1 isoform, HIF-1Z, compared with HIF-1. The 11th and 13th exons were directly joined, which generated an immediate termination codon and a new frame in the 13th exon. This alternative splicing introduces four new amino acids following the Gln⁵⁵³ of HIF-1. It translates into a 557 amino acid polypeptide. Compared with HIF-1, it conserves both bHLH and PAS but loses a part of the ODD domain, TAD and the NLS motif.