In molecular biology, a CCAAT box (also sometimes abbreviated a CAAT box or CAT box) is a distinct pattern of nucleotides with GGCCAATCT consensus sequence that occur upstream by 60–100 bases to the initial transcription site. The CAAT box signals the binding site for the RNA transcription factor, and is typically accompanied by a conserved consensus sequence. It is an invariant DNA sequence at about minus 70 base pairs from the origin of transcription in many eukaryotic promoters. Genes that have this element seem to require it for the gene to be transcribed in sufficient quantities. It is frequently absent from genes that encode proteins used in virtually all cells. This box along with the GC box is known for binding general transcription factors. Both of these consensus sequences belong to the regulatory promoter. Full gene expression occurs when transcription activator proteins bind to each module within the regulatory promoter. Protein specific binding is required for the CCAAT box activation. These proteins are known as CCAAT box binding proteins/CCAAT box binding factors. A CCAAT box is a feature frequently found before eukaryote coding regions, but is not found in prokaryotes. Consensus sequence In the direction of transcription of the template strand, the consensus sequence, or the calculated order of the most frequent residues, for the CAAT box was 3'-TG ATTGG (T/C)(T/C)(A/G)-5'. The use of parentheses denotes that either base is present, but it is not specified as to their relative frequencies. For example, "(T/C)" would mean that either thymine or cytosine are preferentially selected for. Within metazoa (animal kingdom), the core binding factor (CBF)-DNA complex retains a high degree of conservation within the CCAAT binding motif, as well as the sequences flanking this pentameric motif. The CCAAT motif in plants (spinach was used in an experiment) differs slightly from metazoa in that it is actually a CAAT binding motif; the promoter lacks one of the two C residues from the pentameric motif, and the artificial addition of the second C has no significant effects on binding activity. Some sequences lack the CAAT-box completely. Secondly, the surrounding nucleotides in plants do not match the consensus sequence above determined by Bi et al. Core promoter The CAAT box is what is known as a core promoter, also known as the basal promoter or simply the promoter, is a region of DNA that initiates transcription of a particular gene. This region, in particular