https://www.ibiology.org/genetics-and-gene-regulation/transcription-factors/

Transcription, the conversion of DNA to RNA, is one of the most fundamental processes in cell biology. However, only about 3% of our total DNA encodes genes to be transcribed. RNA polymerase II, the enzyme that transcribes DNA to RNA, relies on a large set of proteins known as transcription factors to recognize the coding sequences and to transcribe the correct genes, in the correct cell type, at the correct time. In Part 1 of his lecture, Tjian gives an overview of the complex and critical role that transcription factors play in regulating gene expression.

How do different cells from the same organism, such as muscle cells, neurons and red blood cells, all of which have identical DNA, have such different phenotypes? Tjian addresses this question in his second lecture, where he expands on the mechanisms of gene regulation.