Housekeeping transcriptional control: the TFIID master regulator

The eukaryotic genome consists of two classes of genes preceded by distinctly different promoter sequences. Housekeeping genes (90%) code for proteins that need to be produced at all times while stress genes (10%) code for proteins that are produced as responses to stress stimuli, such as starvation or infection. The PIC has a fundamentally different composition on these two classes of genes; 40% of the protein mass is unique in each complex because the one mega Dalton TFIID molecule exclusively regulates housekeeping genes. Most transcription research has focused on stress genes because the reaction is simpler to reconstitute. Biochemical and structural studies describing transcription initiation on housekeeping promoters are non-existent despite their fundamental importance to cellular biology.