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Chapter 7

Microbial Genetics

Book Version 6
By Boundless
Boundless Microbiology
Microbiology
by Boundless
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Section 1
Genes
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Bacterial Genomes

Bacterial genomes are smaller in size (size range from 139 kbp to 13,000 kpb) between species when compared with genomes of eukaryotes.

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DNA Replication in Prokaryotes

Prokaryotic DNA is replicated by DNA polymerase III in the 5' to 3' direction at a rate of 1000 nucleotides per second.

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Gene Inversion

Gene Inversion utilizes recombinases to invert DNA sequences, resulting in an ON to OFF switch in the gene located within this switch.

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Slipped-Strand Mispairing

Slipped strand mispairing (SSM) is a process that produces mispairing of short repeat sequences during DNA synthesis.

Section 2
Prokaryotic Genomes
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Bacterial Chromosomes in the Nucleoid

The nucleoid is an irregularly-shaped region within the cell of a prokaryote that contains all or most of the genetic material.

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Supercoiling

DNA supercoiling refers to the over- or under-winding of a DNA strand, and is an expression of the strain on that strand.

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Size Variation and ORF Contents in Genomes

An open reading frame (ORF) is the part of a reading frame that varies in size and content in bacterial genomes.

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Bioinformatic Analyses and Gene Distributions

Bioinformatics is the study of methods for storing, retrieving and analyzing biological data.

Section 3
DNA Replication
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Basics of DNA Replication

DNA replication uses a semi-conservative method that results in a double-stranded DNA with one parental strand and a new daughter strand.

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DNA Replication in Eukaryotes

DNA replication in eukaryotes occurs in three stages: initiation, elongation, and termination, which are aided by several enzymes.

Section 4
Plasmids
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Introduction to Plasmids

A plasmid is a small DNA molecule that is physically separate from, and can replicate independently of, chromosomal DNA within a cell.

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Types of Plasmids and Their Biological Significance

Plasmids are commonly used to multiply (make many copies of) or express particular genes.

Section 5
RNA Synthesis: Transcription
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Elongation and Termination in Eukaryotes

Elongation synthesizes pre-mRNA in a 5' to 3' direction, and termination occurs in response to termination sequences and signals.

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The Promoter and the Transcription Machinery

When transcription factors bind to the promoter region, RNA polymerase is placed in an orientation that allows transcription to begin.

Section 6
Translation: Protein Synthesis
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Processing of tRNAs and rRNAs

rRNA and tRNA are structural molecules that aid in protein synthesis but are not themselves translated into protein.

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The Protein Synthesis Machinery

Protein synthesis, or translation of mRNA into protein, occurs with the help of ribosomes, tRNAs, and aminoacyl tRNA synthetases.

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Prokaryotic Transcription and Translation Are Coupled

Prokaryotic transcription occurs in the cytoplasm alongside translation and can occur simultaneously.

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The Incorporation of Nonstandard Amino Acids

Aside from the 22 standard amino acids, there are many other amino acids that are called non-proteinogenic or non-standard.

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Unsticking Stuck Ribosomes

Ribosomes can get stuck on mRNAs, cells have ways of unsticking them.

Section 7
Protein Modification, Folding, Secretion, and Degradation
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mRNA Processing

Eukaryotic pre-mRNA receives a 5' cap and a 3' poly (A) tail before introns are removed and the mRNA is considered ready for translation.

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Denaturation and Protein Folding

Denaturation is a process in which proteins lose their shape and, therefore, their function because of changes in pH or temperature.

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Protein Folding, Modification, and Targeting

In order to function, proteins must fold into the correct three-dimensional shape, and be targeted to the correct part of the cell.

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Regulating Protein Activity and Longevity

A cell can rapidly change the levels of proteins in response to the environment by adding specific chemical groups to alter gene regulation.

Section 8
Archaeal Genetics
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Chromosomes and DNA Replication in the Archaea

Archaea usually have a single circular chromosome.

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Shared Features of Bacteria and Archaea

Most of the metabolic pathways, which comprise the majority of an organism's genes, are common between Archaea and Bacteria.

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Shared Features of Archaea and Eukaryotes

Archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes than prokaryotes.

Section 9
Eukaryotic Genetics
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The Role of the Cell Cycle

The cell cycle allows multiicellular organisms to grow and divide and single-celled organisms to reproduce.

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The Relationship Between Genes and Proteins

Proteins, encoded by individual genes, orchestrate nearly every function of the cell.

Section 10
Mutation
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DNA Repair

Most mistakes during replication are corrected by DNA polymerase during replication or by post-replication repair mechanisms.

Section 11
Genetic Transfer in Prokaryotes
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Generalized Recombination and RecA

In homologous recombination, a type of genetic recombination, nucleotide sequences are exchanged between two similar molecules of DNA.

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Bacterial Transformation

Transformation is the direct uptake, incorporation and expression of exogenous genetic material from its surroundings.

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Bacterial Transduction

Transduction is the process by which DNA is transferred from one bacterium to another by a virus.

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Prokaryotic Reproduction

Prokaryotes reproduce asexually by binary fission; they can also exchange genetic material by transformation, transduction, and conjugation.

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Complementation

Complementation refers to a relationship between two different strains of an organism which both have homozygous recessive mutations.

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Gene Transfer in Archaea

Archaea are distinct from bacteria and eukaryotes, but genetic material can be transferred between them and between Archaea themselves.

Section 12
Tools of Genetic Engineering
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Recombinant DNA Technology

Molecular cloning permits the replication of a specific DNA sequence in a living microorganism.

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Selection

A selectable marker is usually a gene that confers resistance to an antibiotic that would otherwise kill the cells.

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Mutation

Mutations are accidental changes in a genomic sequence of DNA; this includes the DNA sequence of a cell's genome or the DNA or RNA sequence.

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Reproductive Cloning

Reproductive cloning, possible through artificially-induced asexual reproduction, is a method used to make a clone of an entire organism.

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Basic Techniques to Manipulate Genetic Material (DNA and RNA)

Basic techniques used in genetic material manipulation include extraction, gel electrophoresis, PCR, and blotting methods.

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Molecular and Cellular Cloning

Molecular cloning reproduces the desired regions or fragments of a genome, enabling the manipulation and study of genes.

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Plasmids as Cloning Vectors

Plasmids can be used as cloning vectors, allowing the insertion of exogenous DNA into a bacterial target.

Section 13
Bioinformatics
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Strategies Used in Sequencing Projects

The strategies used for sequencing genomes include the Sanger method, shotgun sequencing, pairwise end, and next-generation sequencing.

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Annotating Genomes

Genome annotation is the identification and understanding of the genetic elements of a sequenced genome.

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Homologs, Orthologs, and Paralogs

Homology describes the relationship between genes and how they are inherited from ancestors.

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Synthesizing DNA

DNA can be synthesized chemically for a number of purposes.

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Amplifying DNA: The Polymerase Chain Reaction

The polymerase chain reaction (PCR) is a method by which DNA is amplified.

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DNA Sequencing Based on Sanger Dideoxynucleotides

Sanger sequencing is based on the incorporation and detection of labeled ddNTPs as terminal nucleotides in DNA amplification.

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Metagenomics

Metagenomics is the study of genetic material derived from environmental samples.

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Reporter Fusions

A reporter fusion is the hybrid of a gene or portion of a gene with a tractable marker.

Section 14
Cloning Techniques
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Putting Foreign DNA into Cells

The methods used to get DNA into cells are varied (e.g., transformation, transduction, transfection, and electroporation).

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Obtaining DNA

When cloning genomic DNA, the DNA to be cloned is extracted from the organism of interest.

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Hosts for Cloning Vectors

The majority of molecular cloning experiments begin with a laboratory strain of the bacterium E. coli (Escherichia coli) as the host.

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Shuttle Vectors and Expression Vectors

An expression vector is generally a plasmid that is used to introduce a specific gene into a target cell.

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Bacteriophage Lambda as a Cloning Vector

Enterobacteria phage λ (lambda phage, coliphage λ) is a bacterial virus that infects the bacterial species Escherichia coli.

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Vectors for Genomic Cloning and Sequencing

In molecular biology, a vector is a DNA molecule used as a vehicle to transfer foreign genetic material into another cell.

Section 15
Genome Evolution
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Gene Families

Gene families are groups of functionally related genes arising from a duplicated gene.

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Genomics and Biofuels

Microbial genomics can be used to create new biofuels.

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Genome Reduction

Genome reduction is the loss of genome size of a species in comparison to its ancestors.

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Pathogenicity Islands

Pathogenenicity islands are discrete genetic loci that encode factors which make a microbe more virulent.

Section 16
Environmental Genomics
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Detecting Uncultured Microorganisms

Using metagenomics, the microbial constituents of the world can be identified by culturing each individual species.

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Viral Genomes in Nature

Viruses are the most abundant biological entity on earth, they outnumber all other lifeforms on earth combined.

Section 17
Molecular Regulation
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Catabolite Activator Protein (CAP): An Activator Regulator

When glucose levels decline in E. coli, catabolite activator protein (CAP) is bound by cAMP to promote transcription of the lac operon.

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The Initiation Complex and Translation Rate

The first step of translation is ribosome assembly, which requires initiation factors.

Section 18
Global Regulatory Mechanisms
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Transcription in Prokaryotes

The genetic code is a degenerate, non-overlapping set of 64 codons that encodes for 21 amino acids and 3 stop codons.

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The trp Operon: A Repressor Operon

The trp operon is a repressor operon that is either activated or repressed based on the levels of tryptophan in the environment.

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The Stringent Response

The stringent response is a stress response that occurs in bacteria in reaction to amino-acid starvation or other stress conditions.

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Repression of Anabolic Pathways

Repression of anabolic pathways is regulated by altering transcription rates.

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The AraC Regulator

The L-arabinose operon, also called ara operon, encodes enzymes needed for the catabolism of arabinose to xylulose 5-phosphate.

Section 19
RNA-Based Regulation
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RNA Regulation and Antisense RNA

Antisense RNAs are single-stranded RNA molecules that can bind and inhibit specific mRNA translation to protein.

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Attenuation

Attenuation is a mechanism utilized by bacteria to regulate unnecessary gene expression.

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Riboswitches

Riboswitches are naturally occurring RNA molecules that can regulate gene expression.

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Regulation of Sigma Factor Activity

The sigma factor is responsible for proper transcriptional initiation.

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Regulation of Sigma Factor Translation

Sigma factors are proteins that regulate gene expression that are controlled at various levels, including at the translational level.

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Proteolytic Degradation

Proteolytic degradation, or proteolysis, is a key factor that controls protein concentration and function.

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Small Regulatory RNAs

Small regulatory RNAs are non-coding RNA molecules that play a role in cellular processes such as activation or inhibition processes.

Section 20
Developmental Regulation
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Sporulation in Bacillus

Sporulation is the last-ditch response to starvation; it is suppressed until alternative responses prove inadequate.

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Caulobacter Differentiation

A Caulobacter is used for studying the regulation of the cell cycle, asymmetric cell division, and cellular differentiation.

Section 21
Sensing and Signal Transduction
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Chemotaxis

Chemotaxis is the phenomenon whereby bacterial cells direct their movements according to certain chemicals in their environment.

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Two-Component Regulatory Systems

Two-component systems couple mechanism to allow organisms to sense and respond to changes in many different environmental conditions.

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Quorum Sensing

Quorum sensing is a system of stimulus and response correlated to population density.

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Control of Transcription in Archaea

Transcription and translation in archaea resemble these processes in eukaryotes more than in bacteria.

Section 22
Genomics and Proteomics
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Microarrays and the Transciptome

The transcriptome is the set of all RNA molecules, including mRNA, rRNA, tRNA, and other non-coding RNA produced in cells.

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Proteomics

Proteomics is the large-scale study of proteins, particularly their structures and functions.

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Metabolomics

Metabolomics is the scientific study of chemical processes involving metabolites.

Section 23
Genetic Engineering Products
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Overview of Biotechnology

Biotechnology is the use of biological techniques and engineered organisms to make products or plants and animals that have desired traits.

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Applications of Genetic Engineering

Genetic engineering means the manipulation of organisms to make useful products and it has broad applications.

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Biochemical Products of Recombinant DNA Technology

Many practical applications of recombinant DNA are found in human and veterinary medicine, in agriculture, and in bioengineering.

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Mammalian Gene Expression in Bacteria

Bacterial genetics can be manipulated to allow for mammalian gene expression systems established in bacteria.

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Mammalian Proteins and Products

Genetic engineering enables scientists to create plants, animals, and microorganisms by manipulating genes.

Section 24
Transgenic Organisms
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Genetically Engineered Vaccines

Genetic engineering can be used to manufacture new vaccines.

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Genetic Engineering in Animals

The purpose of genetic engineering in animals is to create animals with special characteristics.

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Biotechnology in Medicine

From manipulation of mutant genes to enhanced resistance to disease, biotechnology has allowed advances in medicine.

Section 25
Molecular Techniques
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Inactivating and Marking Target Genes with Transposons

Transposons allow genes to be transferred to a host organism's chromosome, interrupting or modifying the function of a gene.

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DNA Sequencing of Insertion Sites

An insertion site is the position at which a transposable genetic element is integrated.

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Northern Blots

Northern blots allow investigators to determine messenger RNA molecular weight and sample content.

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Western Blots

The Western blot technique determines protein molecular weight and measures protein abundance in different samples.

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DNA Mobility Shifts

DNA mobility shift assay is a technique for studying gene regulation and determining protein-DNA interactions.

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Purifying Proteins by Affinity Tag

Protein tags are peptide sequences genetically grafted onto a recombinant protein.

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Primer Extension Analysis

Primer extension is used to map the 5' ends of DNA or RNA fragments.

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DNA Protection Analysis

DNA protection or "footprinting" analysis is a powerful technique for identifying the nucleotides involved in a protein-DNA interaction.

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Whole-Genome DNA-Binding Analysis

Whole-genome DNA-binding analysis is a powerful tool for analyzing epigenetic modifications and DNA sequences bound to regulatory proteins.

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Two-Hybrid Analysis

The two-hybrid method detects the interaction of two proteins by their ability to reconstitute the activity of a split transcription factor.

Section 26
Cell Physiology Techniques
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Mapping Protein-Protein Interactions

Mapping protein-protein interactions gives us a better understanding of molecular mechanisms inside the cell.

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Tracking Cells with Light

Advanced technology enables tracking cells with light by introducing fluorescent or luminescent reporter genes into the cells' genome.

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Multiplex and Real-Time PCR

Multiplex and real-time PCR are molecular techniques designed to amplify nucleic acid sequences in a quantitative manner.

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Phage Display

Phage display is a laboratory tool based on cloning DNA sequences into a phage which presents proteins encoded by that DNA on its surface.

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Microbial Genetics
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