Molecular mechanism of hypoxia-inducible factor 1 alpha-p300 interaction -A leucine-rich interface regulated by a single cysteine

Hypoxia-inducible factor Icu (HIF1 alpha) plays a pivotal role in embryogen esis, angiogenesis, and tumorigenesis. HIF1 alpha -mediated transcription r equires the coactivator p300, at least in part, through interaction with th e cysteine- and histidine-rich 1 domain of p300. To understand the molecula r basis of this interaction, we have developed a random mutagenesis screen in yeast approach for efficient identification of residues that are functio nally critical for protein interactions. As a result, four residues (Leu-79 5, Cys-800, Leu-818, and Leu-822) in the C-terminal activation domain of HI F1 alpha have been identified as crucial for HIF1 transactivation in mammal ian systems. Moreover, data from residue substitution experiments indicate the stringent necessity of leucine and hydrophobic cysteine for C-terminal activation domain function. Likewise, Leu-344, Leu-345, Cys388, and Cys-393 in the cysteine- and histidine-rich 1 domain of p300 have also been shown to be essential for the functional interaction, We propose that hypoxia-ind uced HIF1 alpha -p300 interaction relies upon a leucine-rich hydrophobic in terface that is regulated by the hydrophilic and hydrophobic sulfhydryls of HIF1 alpha Cys-800.