28.1 Proteins and RNAs of Gene Regulation Flashcards
Definition of Housekeeping Genes, example
Genes for products that are required at all times, for example enzymes in metabolic pathways.
Definition of Constitutive Gene Expression
Expression of a Gene at approximately constant levels.
Regulation of housekeeping genes
Strongly influenced by RNA polymerase - promoter interaction, and thus differences in a promoter may be the only level of regulation for these genes.
The different types of RNAs and proteins that regulate transcription initiation
specificity factors, repressors, activators, ncRNAs (non-coding RNAs), and lncRNAs (long non-coding RNAs).
Specificity factors
Proteins that increase specificity of RNA polymerase for promoter(s).
Repressors
Protein that hinders access of RNA polymerase to promoter (keeps polymerase from binding).
Activators
Protein that enhances the RNA polymerase - promoter interaction (easier binding).
ncRNAs
Non-coding RNAs, RNAs that do not code for functional proteins.
lncRNAs
Long non-coding RNAs, non-coding RNAs longer than 200 nucleotides.
Bacterial specificity factor (with example)
Amino acid sequences that mediates promoter recognition and binding. The sigma subunit of RNA polymerase of E. coli, most promoters are recognized by the sigma 70.
Eukaryotic specificity factors
Some of the general proteins involved in transcription may be seen as specificity factors, for example the TATA binding protein (TBP).
Operators
Binding site for repressors, usually located near promoter
Effectors
Molecules or proteins that affects how repressor (or activator) binds to DNA, induces conformational change.
Negative regulation
Regulation by repressors
Differences in repressors between bacteria and eukaryots
Negative regulation is less common in eukaryots, except lower eukaryots like yeast, the binding-site for repressors in eukaryots may be farther from the promoter than in bacteria.
Positive regulation
Regulation by activators, enhances transcription. More common in eukaryots where it is situated some distance from the promoter.
Architectual regulators
Protein that binds between promoter and activator/repressor to bend or loop the DNA so these sites are brought closer.
Co-activators
Proteins that mediate interaction between RNA polymerase and the activator. This mechanism may be blocked by repressors.
Difference between transcription state in bacteria and eukaryots
Bacterial transcription is on by default, and is subject to negative regulation. Transcription in eukaryots is off by default (DNA packaging) and is subject to positive regulation.
Operon
A cluster of genes that are regulated together. Polycistronic mRNA in bacterie - multiple genes on the same transcript.
Regulation of the lac-operon
Lac operon contains genes for beta-galactosidase (LacZ), galactose permease (LacY), thiogalactosidase transacetylase (LacA). Negatively regulated in absence of lactose. LacI has its own promoter, codes for repressor protein that binds to main operator of the Lac operon. Allolactose is an inducer for lac operon.
