Gene Regulation & Mobilization

Gene Expression

Process by which genetic information is used to produce functional RNA or proteins.

Constitutive Gene

Gene that is continuously expressed regardless of environmental conditions.

Regulated Gene

Gene expressed only under specific environmental or cellular conditions.

Inducible Gene

Gene activated by an inducer and typically involved in catabolic pathways.

Inducer

Small effector molecule that activates expression of an inducible gene.

Repressible Gene

Gene whose expression is inhibited by a corepressor and typically involved in anabolic pathways.

Corepressor

Small effector molecule that activates a repressor to inhibit gene expression.

β-Galactosidase

Enzyme encoded by lacZ that hydrolyzes lactose into glucose and galactose.

Allolactose

Lactose derivative that acts as the inducer of the lac operon by inactivating the LacI repressor.

Transcription Factor

Regulatory protein that controls transcription by influencing RNA polymerase activity.

Repressor

Regulatory protein that binds the operator and blocks transcription initiation.

Activator

Regulatory protein that binds upstream of a promoter to increase transcription initiation.

Basal (Leaky) Transcription

Low level of gene expression that occurs even when a gene is repressed.

Promoter Strength

Degree of transcriptional activity determined by similarity of a promoter to the consensus sequence.

Operon

Cluster of functionally related genes controlled by a single promoter and transcribed as a polycistronic mRNA.

Lac Operon

Inducible operon that controls lactose uptake and metabolism in bacteria.

lacZ

Gene encoding β-galactosidase.

lacY

Gene encoding lactose permease that transports lactose into the cell.

lacA

Gene encoding thiogalactoside transacetylase.

Lactose Permease

Membrane protein encoded by lacY that transports lactose into bacterial cells.

Thiogalactoside Transacetylase

Enzyme encoded by lacA involved in lactose operon function.

LacI Repressor

Regulatory protein that binds the lac operator and represses transcription in the absence of lactose.

Catabolite Activator Protein (CAP)

Global transcriptional activator that stimulates gene expression when glucose is absent.

Catabolite Repression

Regulation in which glucose suppresses expression of alternative carbon utilization genes such as the lac operon.

Trp Operon

Repressible operon containing genes required for tryptophan biosynthesis.

TrpR Repressor

Regulatory protein that represses the trp operon when activated by tryptophan.

Attenuation

Regulatory mechanism in which transcription termination is controlled by alternative RNA secondary structures in the leader sequence.

Leader Sequence

Regulatory region upstream of structural genes that controls attenuation in the trp operon.

Anti-Termination Structure

RNA stem-loop that allows transcription to continue under low tryptophan conditions.

Terminator Stem-Loop

RNA secondary structure that causes premature termination of transcription under high tryptophan conditions.

RNA Thermometer

RNA secondary structure that regulates translation in response to temperature changes.

Shine-Dalgarno Sequence

Ribosome-binding site in bacterial mRNA required for translation initiation.

Gene Mobilization

Movement of genetic material within or between organisms.

Vertical Gene Transfer (VGT)

Transmission of genetic material from parent to offspring during reproduction.

Genetic Recombination

Rearrangement or exchange of DNA sequences that produces new genetic combinations.

Horizontal Gene Transfer (HGT)

Transfer of genetic material between independent mature cells without reproduction.

Homologous Recombination

Exchange of DNA between molecules with identical or highly similar sequences.

Site-Specific Recombination

Recombination that occurs only at specific DNA target sequences through the action of recombinases.

Conjugation

Horizontal gene transfer through direct cell-to-cell contact.

Conjugative Plasmid

Self-transmissible plasmid that carries genes required for conjugation.

Plasmid

Small circular DNA molecule that replicates independently of the bacterial chromosome.

Origin of Replication (OriR)

DNA sequence at which a plasmid begins replication.

F Factor (F Plasmid)

Conjugative plasmid of Escherichia coli that mediates bacterial conjugation.

Sex Pilus

Surface appendage that establishes contact between donor and recipient cells during conjugation.

Type IV Secretion System (T4SS)

Protein complex that transfers DNA or proteins during conjugation and other secretion processes.

Transfer (tra) Operon

Cluster of genes encoding proteins required for bacterial conjugation.

Origin of Transfer (oriT)

DNA sequence where plasmid transfer begins during conjugation.

Relaxosome

Protein complex that nicks plasmid DNA at oriT to initiate conjugative transfer.

Rolling-Circle Replication

DNA replication mechanism that replaces the transferred DNA strand during conjugation.

Episome

Plasmid capable of existing independently or integrated into the bacterial chromosome.

Insertion Sequence (IS)

Simple mobile genetic element containing a transposase gene flanked by inverted repeats.

Transformation

Horizontal gene transfer involving uptake of free extracellular DNA.

Competent Cell

Cell capable of taking up extracellular DNA from its environment.

Lytic Bacteriophage

Phage that immediately replicates and lyses its bacterial host.

Lysogenic Bacteriophage

Phage that integrates into the bacterial chromosome and remains dormant as a prophage.

Transduction

Horizontal gene transfer mediated by bacteriophages.

Generalized Transduction

Transfer of random bacterial DNA by lytic bacteriophages due to packaging errors.

Specialized Transduction

Transfer of specific bacterial genes adjacent to a prophage insertion site by lysogenic bacteriophages.

Prophage

Bacteriophage genome integrated into the bacterial chromosome.

Griffith Experiment

Experiment demonstrating that bacteria can be transformed by a transforming principle.

Avery–MacLeod–McCarty Experiment

Experiment demonstrating that DNA is the transforming principle and genetic material.

Mobile Genetic Element

DNA sequence capable of moving within or between genomes.

Transposon

Mobile genetic element capable of moving between DNA locations.

Simple (Cut-and-Paste) Transposition

Transposition mechanism in which a transposon is excised and inserted into a new DNA site.

Replicative (Copy-and-Paste) Transposition

Transposition mechanism in which a transposon is copied while the original remains at its original location.

Inverted Repeat

Short repeated DNA sequence flanking a transposon in opposite orientations.

Direct Repeat

Short repeated DNA sequence generated at the target site during transposon insertion.

Transposase

Recombinase enzyme that catalyzes transposition.

Agrobacterium tumefaciens

Plant pathogenic bacterium that transfers DNA into plant cells and causes crown gall disease.

Ti Plasmid

Tumor-inducing plasmid of Agrobacterium tumefaciens that mediates DNA transfer to plants.

T-DNA

Transfer DNA segment of the Ti plasmid that integrates into the plant genome.

Crown Gall Disease

Plant tumor disease caused by Agrobacterium tumefaciens through T-DNA transfer.

Opines

Specialized nutrients produced by transformed plant cells and utilized by Agrobacterium tumefaciens.