CCAATbinding

CCAAT-binding refers to transcription factors that recognize the CCAAT box, a common promoter element found in many eukaryotic genes. The most well characterized CCAAT-binding factors are the heterotrimeric NF-Y complex in animals and plants, and the Hap (CBAF) complex in budding yeast. These factors bind DNA with high affinity to CCAAT motifs and often cooperate with other transcriptional regulators to control gene expression.

In mammals and other higher eukaryotes, NF-Y is a trimer composed of NF-YA, NF-YB, and NF-YC. NF-YB and NF-YC form a histone-fold dimer that associates with NF-YA, which provides sequence-specific DNA recognition. The complex binds as a trimer to the CCAAT box, typically bending the DNA and influencing nucleosome positioning. NF-Y regulates a broad set of genes, including those involved in cell cycle progression, metabolism, differentiation, and stress responses. It frequently operates in conjunction with other transcription factors and can act as a pioneer factor in chromatin remodeling.

In budding yeast and some other fungi, the CCAAT-binding factor is the Hap complex, comprising Hap2, Hap3, Hap4, and Hap5. Hap2/3/5 form the DNA-binding core, while Hap4 serves as a transcriptional activation subunit. The Hap complex regulates mitochondrial respiration and energy metabolism by activating genes encoding components of the electron transport chain, especially under respiratory conditions and appropriate environmental signals such as oxygen availability and heme status.

Overall, CCAAT-binding factors are essential, evolutionarily conserved regulators that connect promoter architecture to cellular metabolism, growth, and environmental responses. Dysregulation of these factors has been linked to various diseases, including cancer, in higher eukaryotes.