The evolutionarily conserved CCAAT binding protein NF-Y is a common regulatory DNA binding protein consisting of three distinct subunits. Unlike yeast and mammals, in which only a single copy of each subunit is encoded, Arabidopsis encodes a multi-gene family for each subunit in its genome. Compared with the NF-Y of mammals or yeast, very little is known about plant NF-Y homologs. Here Arabidopsis NF-YA subunits were isolated to determine whether they could form a heterotrimeric NF-Y complex with mammalian NF-YB and NF-YC. This resultant chimeric NF-Y complex had DNA binding ability to the same CCAAT sequences as those of the other life systems. Therefore, it is possible that plant NF-Y homologs might have biochemical characteristics similar to mammalian NF-Y, thereby suggesting its functional conservation among organisms.