Conjugation uses

Triparental conjugation

Conjugation can still occur using recombinant plasmid lacking the required tra genes and a helper plasmid with the genes. More room in the recombinant plasmid for a desired DNA fragment.

Transposition

Movement of DNA via mobile genetic elements. Some genes can move from 1 part of genome to another at low frequencies. Transposable elements can move within and between genomes and is carried out by transposable elements.

Barbara McClintock

She first detected transposition in corn

Transposition can be subdivided into?

Insertion sequences, transposons

Insertion sequences

Encode only the proteins needed for transposition. A transposable element. Can be found on F

Transposons

Contain other genes in addition to those needed for transposition. A transposable element

Mechanisms of transposition

Replicative, non-replicative

Transposition requires what kind of genes?

Transposase and resolvase

Replicative transposition

Copies the element and moves the copy to another location

Non-replicative transposition

Cuts and pastes the element into a new location

Transposition can be used to disrupt ___ and observe ___

Functional genes, phenotypic changes

Suicide vector plasmid carrying the transposon. What does the recipient cell get and what happens?

Recipient cell gets plasmid, plasmid can’t replicate. Transposition can still occur at random. Screening and/or selection for desired disruption follows.

Transduction process

Virus accidentally packages a fragment of host cell DNA (transducing particles). Virus delivers that fragment instead of viral DNA to next cell. Virus is usually unable to replicate b/c it lacks viral genome. Homologous recombination must occur.

Historically, co-transduction frequency was used to?

Map bacterial genomes.

Co-transduction frequency

Genes that were closer to a known “marker” gene would be transduced with that marker more frequently than ones farther away.

Co-transduction frequency can be used to modify bacteria. Experimental modification of a common _____ to express and secrete _____.

vaginal tract microbe, a chemokine with anti-HIV activity

Co-transduction frequency can be used to modify bacteria. Work has only been performed in ___ so far

vitro

Transposable elements, such as transposons and insertion sequencies, contain genes that do what?

Encode transposase enzymes, which recognize terminal inverted repeat sequences

Transposition is a recombination process, but it doesn’t involve ____, but rather ____.

homologous recombination, site-specific recombination

Why is transposition useful for mutagenesis? What kind of experiment can be set up as a result?

If a transposon inserts within a gene, it’ll disrupt function of that gene. It’s possible to set up a transposition experiment where transposon that confers antibiotic resistant colonies contain a transposon insertion at a unique location. The insertion containing colonies can then be screened for desired phenotype.

Bacteriophage are sometimes able to transfer genes between bacterial strains by ______.

transduction

Generalized transduction involves?

Transfer of DNA from any region of the chromosome

What are transducing particles and how do they occur? What can happen to them after?

When lytic bacteriophage DNA is packaged into phage particles, some of the host cell’s DNA can be accidentally packaged into a small proportion of the phage particles (rare) —they only contain host cell DNA, no phage DNA. They can inject packaged DNA from host cell into an appropriate recipient cell, where it’s free to recombine into recipient cell’s genome.

Specialized transduction

The formation of transducing particles associated with lysogenic phage

Generalized vs specialized transduction

For lytic bacteriophage vs lysogenic phage

Specialized transduction is associated with lysogenic bacteriophage infections. What happens to the bacteriophage’s genome? i.e. what is the process of transduction here?

Bacteriophage genome integrates into host genome at specific location. When it excises again, it occasionally does so imperfectly, taking with it a little bit of bacterial genome. When this happens, very specific genes close to the integrate site are taken with it into the bacteriophage particle, along with lots of virus DNA.

Specialized transduction involves packaging with ______ contained within _____ particles. When specialized transduction happens with a lysogenic virus, ___ particles are transducing particles. Transducing particles have ____ ___ + host genome.

site-specific genes, transducing, all, virus genes