BIBC 100 Study Guide - Midterm Guide: Lac Repressor, Dna-Binding Domain, Alpha Helix
Document Summary
Regulating transcription of genes from dna is essential to life: proteins that bind to dna important. Dna binding domain: helix-turn-helix (hth) common in prokaryotes: structural features, cro: alpha + beta protein, 3 alpha helices and 3 beta strands. Helices form hth turned structure: 2 monomers form a dimer through interactions of beta sheets, lambda repressor, 5 alpha helices. First 3 participate in hth and last 2 form dimer: contact with dna, cro: alpha 3 (recognition helix) sits directly in major groove. 2 dimers of cro 34 a apart, so can bind 2 successive major groove sites on same side of dna. If lambda repressor present, blocks cro promoter and encourages transcription of lambda repressor and vice versa. Binding of tryptophan means that enough tryptophan is present and production should stop. When tryptophan binds, angle of head changes to allow contact with 2 consecutive major grooves of dna on the same side of the strand.
