Regulation of gene expression - concept Flashcards
cis-acting elements and trans-acting factors
Gene expression is regulated because microorganism adapt
Mutations affecting regulated expression of genes can be in cis (same gene/genetic element) or in trans (in different gene/genetic element)
Cis mutations identify DNA/RNA sequences that affect gene regulation
Trans mutations identify protein or RNA factors that regulate gene expression
Most genes regulated at transcription level
Transcription regulation primary level control most genes
(need to go back over this lecutre) limits wasteful production unreuited biomolecules
Trans-acting factors can act to activate or repress transcription
Trans-acting factors act to up or downregulate expression
Trans-acting activators - factors causes activation - positive control
Activators promote expression at weak promoters
Trans-acting repressor - factors causing down regulation - negative control
Activators interact with alpha-subunit of RNA polymerase and promote DNA binding
The promoter region of E.coli genes
E.coli gene promoters have conserved bipartite sequences, found at approximately 35 and 10 nucleotides upstream (5’) of where transcription starts
Promoters with sequences close to consensus sequence are strong promoters
Weak promoters have divergent sequence from consensus (most common sequence where promoters occur)
Expression of enzyme-coding genes can be regulated by substrate/product availability
Inducers - substrates that mediate upregulated expression of enzymes
Corepressors - product mediating downregulated expression of enzymes
Genes under positive (activator) or negative (repressor) control can be inducible or repressible
Gene expression can be regulated at levels of RNA processing
Pre-mRNA splicing can occur in different patterns
Can lead to production two distinct proteins from same pre-mRNA
There can be a productive and non-productive pathway
The mRNA can be degraded, blocking expression
Alternative splicing of pre-mRNA generates distinct mRNAs from single transcript
Common from alternative splicing involves inclusion of either one or other adjacent exon - mutation exclusive splicing
Exon inclusion or exclusion promoted by splicing activator or repressor proteins that bind to specific sequence within pre-mRNA
Gene expression can be regulated at level of translation
Translation can be regulated globally, typically occurs at initiation step
Specific transcript can be regulated independently by binding of proteins or small molecules
Recognition SD sequence need for regulation to start in Pro
Can alter structure of pathway in RNA and stops expression
Temperature shift can cause localised shifts in RNA which can uncover structures or sequences, e.g. could uncover or cover SD sequence
Autoregulation of gene expression
Gene product influences own expression
Some ribosomal proteins in E. coli bind to own mRNA and mask SD sequence
5’ leader structurally similar to region within rRNA that is binds to
When to much created can bind other similar sights along mRNA which normally block SD sequence and can stop transcription and translation
Example of negative feedback
Protein function can be regulated by post-transcriptional modifications
Many proteins processed or post-translationally modified
Phosphorylation of serine, threonine or tyrosine residues in most common form post-translational modification
Phosphorylation often affect proteins ability to interact with other molecules
Phosphorylation readily reversible
Phosphorylation driven by protein kinases and reversed by phosphatases
