the CAAT box and CCAAT sequence, which is thought to play a pivotal role in the (MLP) of subgroup C human adenoviruses, in species with a deficient CAAT sequence. The transcription initiation at mutant MLP species was significantly reduced compared with that of the wild type or species in which there was a CAAT mutant. The failure to restore the normally functional adenoviruses, exhibited by a CAAT box, is consistent with the idea that the CAAT box plays a vital role in the adenovirus MLP and is preferred over other transcriptional elements. CCAAT in plants These core binding factors, or nuclear factors (NF-Y), are composed of three subunits – NF-YA, NF-YB, and NF-YC. Whereas in animals each NF-Y subunit is encoded by a single gene, there has been a diversification in plants in both structure and function. Families of NF-Y consist of between eight and 39 members per subunit. A large reason for this diversification is because of gene duplications and tandem duplications, which have helped contribute to the larger family sizes of NF-Y compared to the single encoded animal nuclear factors. Each subunit contains an evolutionarily conserved part – the C-terminal of NF-YA, the central part of NF-YB, and the N-terminal of NF-YC, greater than 70% of these across species remains conserved. Neighboring regions however are generally not conserved. NF-YA subunit The NF-YA family encodes transcription factors that are variable in length (between 207 and 347 amino acids for M. truncatula). The NF-YA proteins are generally characterized by two domains that are strongly conserved in all higher eukaryotes investigated to date. The first domain (A1) contains 20 amino acids that forms an alpha helix that appears significant in its interactions with NF-YB and NF-YC. The second domain (A2) is adjacent to the A1 domain by a conserved linker sequence is a sequence of 21 amino acids vital in the specific DNA to CCAAT box binding. The A1 and A2 domains are conserved towards the C-terminus of mammals, but occupy a more central region in plant NF-YA subunits. In plants, the NF-YA subunit has evolved to regulate the development of a facultative root organ only present in leguminous plants and shown to be expressed in root tissue. It was shown to have drought-resistant-like properties, becoming upregulated during drought stress in the roots and leaves of Arabidopsis. NF-YA mutants have shown a loss of function and a hypersensitivity to drought-like conditions,