In Saccharomyces cerevisiae, the haem-activated protein complex Hap2/3/4/5 plays a major role in the transcription of genes involved in respiration [3]. Hap4_Hap_bind is the essential domain of Hap4 which allows it to associate with Hap2, Hap3 and Hap5 to form the Hap complex [2].

1: Identification and characterization of HAP4: a third component of the CCAAT-bound HAP2/HAP3 heteromer. Forsburg SL, Guarente L; Genes Dev. 1989;3:1166-1178. PMID:2676721

2: Assembly of the Hap2p/Hap3p/Hap4p/Hap5p-DNA complex in Saccharomyces cerevisiae. McNabb DS, Pinto I; Eukaryot Cell. 2005;4:1829-1839. PMID:16278450

3: Hap4 is not essential for activation of respiration at low specific growth rates in Saccharomyces cerevisiae. Raghevendran V, Patil KR, Olsson L, Nielsen J; J Biol Chem. 2006;281:12308-12314. PMID:16522629