Genetics Chapter 14: Gene Regulation in Bacteria
stem loop that acts as a terminator
3-4 stem loop
regions of the lac operon
CAP site, promoter (lacP), operator site (lacO), three structural genes (lacZ,lacY, and lacA), and a terminator
Three operator sites for lac operon
O1: located slightly downstream from the promoter O2: located farther downstream in the lacZ coding sequence O3: located slightly upstream from the promoter When O2 and O3 are missing, repression is greatly reduced. When O1 is missing, repression is nearly abolished. the lac repressor can bind to O1 and O2, or O3 and O1, but not O2 and O3. The DNA forms a loop
CAP site
a DNA sequence recognized by an activator protein called the catabolite activator protein (CAP)
operon
a group of two or more genes under transcriptional control of a single promoter
attenuation
a mechanism of genetic regulation, seen in trp operon, in which a short RNA is made but its synthesis is terminated before RNA polymerase can transcribe the rest of the operon.
lactose permease
a membrane protein required for the active transport of lactose into the cytoplasm of the bacterium
lac repressor
a protein that is important for the regulation of the lac operon. functions as a homotetramer, a protein composed of 4 identical subunits.
activator
a regulatory protein that increases the rate of transcription
attenuator sequence
a segment of DNA that is important in facilitating attenuation. encodes the leader peptide (14 amino acids), stops transcription soon after it has begun
operator site
a sequence of bases that provides a binding site for a repressor protein
corepressor
a small molecule that binds to a repressor protein, thereby causing the protein to bind to DNA
effector molecule
a small molecule that does not bind directly to the DNA; it exerts it's effects by binding to an activator or a repressor. This causes a conformational change in the regulatory protein and affects whether or not it can bind to the DNA
repressor
a type of regulatory protein that binds to the DNA and inhibits transcription
antisense RNA
an RNA strand that is complimentary to a strand of mRNA
inducer
an effector molecule that causes transcription to increase. may accomplish this in two ways: bind to a repressor protein and prevent it from binding to DNA, or bind to and activator protein and cause it to bind to the DNA.
B-galactose
an enzyme that cleaves lactose into glucose and galactose. as a side reaction, B-galactose also converts lactose into allolactose, a structurally similar molecule that works as an effector molecule to regulate the lac operon
galactoside transacetylase
an enzyme that covalently modifies lactose and lactose analogs.
inhibitor
binds to an activator protein and prevents it from binding to DNA
posttranslational covalent modification
covalent attachment of a molecule to a protein after it has been synthesized via ribosomes
polycistronic RNA
encoded by an operon; an RNA that contains a sequence for two or more genes
lacZ
encodes B-galactose
lacA
encodes galactoside transacetylase
lacY
encodes lactose permease
lacI gene
encodes the lac repressor
trpR gene
encodes the trp repressor protein.
allosteric enzyme
enzyme that contains two binding sites: catalytic site and regulatory site
antitermination
function of certain proteins such as N protein in bacteria that prevents transcriptional termination
repressible genes
genes that are regulated by corepressors and inhibitors which reduce the rate of transcription
cyclic AMP (cAMP)
in bacteria, a small effector molecule that binds to CAP (catabolite activator protein), in eukaryotes cAMP functions as a second messenger in a variety of intracellular signaling pathways
effects of glucose and/or lactose on lac operon
in the presence of just lactose: cAMP levels are high, and transcription is high in the absence of glucose and lactose: cAMP is high, transcription is low in the presence of both: cAMP is low, transcription is low in the presence of only glucose: cAMP low, transcription low
riboswitch
mechanism for regulating transcription, translation, RNA stability and splicing in which RNA molecule can switch between two secondary conformations based on whether or not a small molecule such as TPP binds to RNA
trpL gene
mediates attenuation
three common processes regulated at the genetic level
metabolism, response to environmental stress, cell division
catabolite regulation
phenomenon in which a catabolite (glucose) represses expression of certain gene (lac operon)
translational repressors
protein that binds to mRNA and inhibits its ability to be translated
translational regulatory protein
recognizes sequences within the mRNA, such as transcription factors recognize DNA sequences
promoter
signals the beginning of transcription of an operon
terminator
signals then end of transcription on an operon
allosteric site
site on a protein where a small effector molecule binds to regulate the function of the protein
allosteric regulation
the action of a small effector molecule such as allolactose binding to an enzyme's allosteric site
feedback inhibition
the final product of a metabolic pathway inhibits an enzyme that acts earlier in the pathway
posttranslational regulation
the functional control of proteins that are already present in the cell rather than regulation of transcription or translation
enzyme adaptation
the observation that a particular enzyme appears within a living cell only after the cell has been exposed to the substrate of that enzyme
gene regulation
the phenomenon in which the level of gene expression can vary under different conditions
negative control
transcriptional regulation by a repressor protein.
positive control
transcriptional regulation by an activator protein
constitutive genes
unregulated genes. Frequently, these genes encode proteins that are continuously needed for the survival of bacterium.
trp repressor protein
when trp levels are very low, the repressor can not bind, allowing transcription. When trp is present, it acts as a corepressor and causes the trp repressor to bind.
