the TATA box and general transcription factors
/ TAH-tah box; G-T-Fs /
Bacteria start transcription with a single helper, but eukaryotic cells turn it into a committee meeting. Before RNA polymerase II will even sit down at a gene, a sequence of specialist proteins must arrive in order, recognize the promoter, bend the DNA, and lay out the seat. The TATA box and the general transcription factors are the cast of that opening scene.
Many eukaryotic promoters contain a TATA box — a short A/T-rich sequence (roughly TATAAA) sitting about 25 to 30 bases upstream of the start. It is recognized not by the polymerase but by a dedicated protein, the TATA-binding protein (TBP), which clamps onto the minor groove and kinks the DNA sharply. TBP is part of a larger factor (TFIID), and its binding nucleates the stepwise arrival of the general transcription factors — a defined set named TFIIA, TFIIB, TFIID, TFIIE, TFIIF, and TFIIH. They are called 'general' because they are needed at essentially every Pol II promoter, regardless of which specific gene it is — they are the basic, always-required machinery, distinct from the gene-specific regulators that fine-tune individual genes. One of them, TFIIH, even carries a motor that helps melt the DNA open and a kinase that releases the polymerase into elongation.
This factor-assembly system is what makes eukaryotic transcription so much more controllable than the bacterial version. Because so many separate proteins must come together correctly, there are many points at which gene-specific activators or repressors can help or hinder, dialling expression up or down with great precision. Not all eukaryotic promoters have a TATA box — many use other core elements instead — but the principle holds: the polymerase is escorted into place by an assembled crew rather than acting alone.
TBP bends a TATA box by nearly 80 degrees, like folding a strip of paper, creating a kink that the other general factors and polymerase then assemble around.
TBP's sharp DNA bend nucleates assembly of the Pol II machinery.
'General' transcription factors are the basal machinery present at essentially every Pol II gene — don't confuse them with the gene-specific transcription factors (activators and repressors) that decide which particular genes are on. The general factors enable transcription; the specific factors regulate it.