The Hershey–Chase experiments were a series of experiments conducted in 1952 by Alfred Hershey and Martha Chase that helped to confirm that DNA is genetic material. While DNA had been known to biologists since 1869, many scientists still assumed at the time that proteins carried the information for inheritance because DNA appeared to be an inert molecule, and, since it is located in the nucleus, its role was considered to be phosphorus storage. In their experiments, Hershey and Chase showed that when bacteriophages, which are composed of DNA and protein, infect bacteria, their DNA enters the host bacterial cell, but most of their protein does not. Although the results were not conclusive, and Hershey and Chase were cautious in their interpretation, previous, contemporaneous, and subsequent discoveries all served to prove that DNA is the hereditary material.
Enterobacteria phage λ is a bacterial virus, or bacteriophage, that infects the bacterial species Escherichia coli. It was discovered by Esther Lederberg in 1950 when she noticed that streaks of mixtures of two E. coli strains, one of which treated with ultraviolet light, was "nibbled and plaqued". The wild type of this virus has a temperate lifecycle that allows it to either reside within the genome of its host through lysogeny or enter into a lytic phase ; mutant strains are unable to lysogenize cells – instead, they grow and enter the lytic cycle after superinfecting an already lysogenized cell.
Virulence is a pathogen's or microbe's ability to infect or damage a host.
Escherichia virus T4 is a species of bacteriophages that infect Escherichia coli bacteria. It is a member of virus subfamily Tevenvirinae and includes among other strains Enterobacteria phage T2, Enterobacteria phage T4 and Enterobacteria phage T6. T4 is capable of undergoing only a lytic lifecycle and not the lysogenic lifecycle.
Phage display is a laboratory technique for the study of protein–protein, protein–peptide, and protein–DNA interactions that uses bacteriophages to connect proteins with the genetic information that encodes them. In this technique, a gene encoding a protein of interest is inserted into a phage coat protein gene, causing the phage to "display" the protein on its outside while containing the gene for the protein on its inside, resulting in a connection between genotype and phenotype. These displaying phages can then be screened against other proteins, peptides or DNA sequences, in order to detect interaction between the displayed protein and those other molecules. In this way, large libraries of proteins can be screened and amplified in a process called in vitro selection, which is analogous to natural selection.
Adhesins are cell-surface components or appendages of bacteria that facilitate adhesion or adherence to other cells or to surfaces, usually the host they are infecting or living in. Adhesins are a type of virulence factor.
Lysogeny, or the lysogenic cycle, is one of two cycles of viral reproduction. Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome or formations of a circular replicon in the bacterial cytoplasm. In this condition the bacterium continues to live and reproduce normally. The genetic material of the bacteriophage, called a prophage, can be transmitted to daughter cells at each subsequent cell division, and at later events can release it, causing proliferation of new phages via the lytic cycle. Lysogenic cycles can also occur in eukaryotes, although the method of DNA incorporation is not fully understood.
Bacterial display is a protein engineering technique used for in vitro protein evolution. Libraries of polypeptides displayed on the surface of bacteria can be screened using flow cytometry or iterative selection procedures (biopanning). This protein engineering technique allows us to link the function of a protein with the gene that encodes it. Bacterial display can be used to find target proteins with desired properties and can be used to make affinity ligands which are cell-specific. This system can be used in many applications including the creation of novel vaccines, the identification of enzyme substrates and finding the affinity of a ligand for its target protein.
Bacteriophage T7 is a bacteriophage, a virus that infects susceptible bacterial cells, that is composed of DNA and infects most strains of Escherichia coli. Bacteriophage T7 has a lytic life cycle and several properties that make it an ideal phage for experimentation.
The Enterobacteria phage P22 is a bacteriophage that infects Salmonella typhimurium. Like many phage viruses, it has been used in molecular biology to induce mutations in cultured bacteria and to introduce foreign genetic material. Upon its discovery, P22 has been used in generalized transduction and is an important tool for Salmonella genetics.
P1 is a temperate bacteriophage that infects Escherichia coli and some other bacteria. When undergoing a lysogenic cycle the phage genome exists as a plasmid in the bacterium unlike other phages that integrate into the host DNA. P1 has an icosahedral head containing the DNA attached to a contractile tail with six tail fibers. The P1 phage has gained research interest because it can be used to transfer DNA from one bacterial cell to another in a process known as transduction. As it replicates during its lytic cycle it captures fragments of the host chromosome. If the resulting viral particles are used to infect a different host the captured DNA fragments can be integrated into the new host's genome. This method of in vivo genetic engineering was widely used for many years and is still used today, though to a lesser extent. P1 can also be used to create the P1-derived artificial chromosome cloning vector which can carry relatively large fragments of DNA. P1 encodes a site-specific recombinase, Cre, that is widely used to carry out cell-specific or time-specific DNA recombination by flanking the target DNA with loxP sites.
fis is an E. coli gene encoding the Fis protein. The regulation of this gene is more complex than most other genes in the E. coli genome, as Fis is an important protein which regulates expression of other genes. It is supposed that fis is regulated by H-NS, IHF and CRP. It also regulates its own expression (autoregulation). Fis is one of the most abundant DNA binding proteins in Escherichia coli under nutrient-rich growth conditions.
Outer membrane receptors, also known as TonB-dependent receptors, are a family of beta barrel proteins named for their localization in the outer membrane of gram-negative bacteria. TonB complexes sense signals from the outside of bacterial cells and transmit them into the cytoplasm, leading to transcriptional activation of target genes. TonB-dependent receptors in gram-negative bacteria are associated with the uptake and transport of large substrates such as iron siderophore complexes and vitamin B12.
Bacteriophage T5 is a caudal virus within the family Siphoviridae. This bacteriophage specifically infects E. coli bacterial cells and follows a lytic life cycle.
Bacteriophage P2, scientific name Escherichia virus P2, is a temperate phage that infects E. coli. It is a tailed virus with a contractile sheath and is thus classified in the genus P2virus, subfamily Peduovirinae, family Myoviridae within order Caudovirales. This genus of viruses includes many P2-like phages as well as the satellite phage P4.
In molecular biology, bacterial DNA binding proteins are a family of small, usually basic proteins of about 90 residues that bind DNA and are known as histone-like proteins. Since bacterial binding proteins have a diversity of functions, it has been difficult to develop a common function for all of them. They are commonly referred to as histone-like and have many similar traits with the eukaryotic histone proteins. Eukaryotic histones package DNA to help it to fit in the nucleus, and they are known to be the most conserved proteins in nature. Examples include the HU protein in Escherichia coli, a dimer of closely related alpha and beta chains and in other bacteria can be a dimer of identical chains. HU-type proteins have been found in a variety of eubacteria and archaebacteria, and are also encoded in the chloroplast genome of some algae. The integration host factor (IHF), a dimer of closely related chains which is suggested to function in genetic recombination as well as in translational and transcriptional control is found in Enterobacteria and viral proteins including the African swine fever virus protein A104R.
T-even phages, also known as the E. coli phages, are a group of double-stranded DNA bacteriophages from the family Myoviridae. Bacteriophage means to "eat bacteria", and phages are well known for being obligate intracellular parasites that reproduce within the host cell and are released when the host is destroyed by lysis. Containing about 160 genes, these virulent viruses are among the largest, most complex viruses that are known and one of the best studied model organisms. They have played a key role in the development of virology and molecular biology.
