Before genes are expressed, they must first be transcribed into mRNA.  To begin this process, proteins must be bound to:
1.  An enhancer site and
2.  A promoter site

Binding of specific proteins to these sites depends on the exact recognition of nucleotide sequences on the DNA molecule.

The TATA box positions RNA polymerase at the start of the site for mRNA transcription.


Some DNA -binding proteins are "positive regulators" which stimulate transcription, while others are "negative regulators" which block transcription.