GC box

A GC box is a conserved nucleotide sequence in eukaryotes with the consensus sequence 5' GGGCGG 3'.

It acts in a similar fashion to an enhancer sequence, binding proteins called Sp1s which further stabilise the preinitiation complex at the promoter of a gene, and thereby increase the rate of transcription of that gene. GC boxes are a type of promoter-proximal element, like the nearby CAAT region. GC boxes are generally located about 110 base pairs upstream of the transcription initiation site.