医学Regulation of gene expression.pptVIP

Regulation of gene expression Concepts Gene Genome Gene expression Specificity of gene expression Temporal specificity also called stage specificity Spatial specificity also called tissue specificity Type of gene expression a. Constitutive expression housekeeping genes. b. Induction and repression The most important stage for the regulation of most genes is transcription initiation. Special DNA sequence Promoter The DNA sequence that RNA-pol can bind and initiate the transcription. Operator The operators are generally near a promoter. b. Regulatory proteins Regulation of Gene Expression in Prokaryotes Common features Prokaryotic genes are polycistron systems The majority of gene regulation is negative. Inducers are used to remove the repression. Operons Structural genes Galactoside permease: transport lactose into the cell across the cell membrane β-Galactosidase: hydrolyze lactose to glucose and galactose or convert lactose to allolactose Thiogalactoside transacetylase: may involved in the detoxification. Situation 1 When lactose is absent, no lac gene is expressed. Situation 2 Inducers Situation 3 When glucose is present, the [cAMP] is low, no CAP-cAMP is formed and the expression of the lac operon is still low. Situation 4 When glucose is absent and lactose is present, the CAP-cAMP complex binds to the CAP site to activate the lac gene. Coordinate regulation Tryptophan (Trp) operon Attenuation of Transcription Regulation of Gene Expression in Eukaryotes Structural features Large genome Monocistron Repeated sequences Split genes Modification of DNA Positive regulation: more accurate regulation and more efficient. Transcription and translation are separated: at different locations. Post-transcriptional modification: more complicated than prokaryotes. Regulation through intercellular and intracellular signals: hormone. Gene Regulatory Sequences Cis-acting elements The gene regulatory sequences are also called