The TATA box is the 5' TATA 3' sequence which is found in the DNA strand of a promoter and is found in the core elements. The TATA box is usually found near the -31--26 region of the promoter and its sequence is T - A -T - A - A/T - A - A/T - A/G. The TATA box is a common promoter sequence recognized by RNA Polymerase II. It is found in both prokaryotes and eukaryotes however in the two it's spacing from the transcriptional start site differs. A eukaryotic cell does not have to have a TATA box and can instead have a combination of different core promoter elements, e.g. initiator element (which is basically just a pyrimidine ring). In mammals ~60-70% of protein coding genes lack the obvious TATA sequence and it is therefore transcription can occur at other start sites, such as CpG islands.