A recombination system has been developed for efficient chromosome engineering in Escherichia coli by using electroporated linear DNA. A defective lambda prophage supplies functions that protect and recombine an electroporated linear DNA substrate in the bacterial cell. The use of recombination eliminates the requirement for standard cloning as all novel joints are engineered by chemical synthesis in vitro and the linear DNA is efficiently recombined into place in vivo. The technology and manipulations required are simple and straightforward. A temperature-dependent repressor tightly controls prophage expression, and, thus, recombination functions can be transiently supplied by shifting cultures to 42 degrees C for 15 min. The efficient prophage recombination system does not require host RecA function and depends primarily on Exo, Beta, and Gam functions expressed from the defective lambda prophage. The defective prophage can be moved to other strains and can be easily removed from any strain. Gene disruptions and modifications of both the bacterial chromosome and bacterial plasmids are possible. This system will be especially useful for the engineering of large bacterial plasmids such as those from bacterial artificial chromosome libraries.

/pdf/an-efficient-recombination-system-for-chromosome-engineering-4acmootzcr.pdf

An efficient recombination system for chromosome engineering in Escherichia coli

We describe a transgenesis platform for Drosophila melanogaster that integrates three recently developed technologies: a conditionally amplifiable bacterial artificial chromosome (BAC), recombineering, and bacteriophage PhiC31-mediated transgenesis. The BAC is maintained at low copy number, facilitating plasmid maintenance and recombineering, but is induced to high copy number for plasmid isolation. Recombineering allows gap repair and mutagenesis in bacteria. Gap repair efficiently retrieves DNA fragments up to 133 kilobases long from P1 or BAC clones. PhiC31-mediated transgenesis integrates these large DNA fragments at specific sites in the genome, allowing the rescue of lethal mutations in the corresponding genes. This transgenesis platform should greatly facilitate structure/function analyses of most Drosophila genes.

https://science.sciencemag.org/content/sci/314/5806/1747.full.pdf

P[acman]: A BAC Transgenic Platform for Targeted Insertion of Large DNA Fragments in D. melanogaster

Regulation of translation via mRNA structure in prokaryotes and eukaryotes.

Synaptic mitochondria are critical for mobilization of reserve pool vesicles at Drosophila neuromuscular junctions.

Recombineering is an efficient method of in vivo genetic engineering applicable to chromosomal as well as episomal replicons in Escherichia coli. This method circumvents the need for most standard in vitro cloning techniques. Recombineering allows construction of DNA molecules with precise junctions without constraints being imposed by restriction enzyme site location. Bacteriophage homologous recombination proteins catalyze these recombineering reactions using double- and single-stranded linear DNA substrates, so-called targeting constructs, introduced by electroporation. Gene knockouts, deletions and point mutations are readily made, gene tags can be inserted and regions of bacterial artificial chromosomes or the E. coli genome can be subcloned by gene retrieval using recombineering. Most of these constructs can be made within about 1 week's time.

https://redrecombineering.ncifcrf.gov/protocols/sharan-2009-nature-protoc.pdf

Recombineering: a homologous recombination-based method of genetic engineering

The bacterial chromosome and bacterial plasmids can be engineered in vivo by homologous recombination using PCR products and synthetic oligonucleotides as substrates. This is possible because bacteriophage-encoded recombination proteins efficiently recombine sequences with homologies as short as 35 to 50 bases. Recombineering allows DNA sequences to be inserted or deleted without regard to location of restriction sites. This unit first describes preparation of electrocompetent cells expressing the recombineering functions and their transformation with dsDNA or ssDNA. It then presents support protocols that describe several two-step selection/counter-selection methods of making genetic alterations without leaving any unwanted changes in the targeted DNA, and a method for retrieving onto a plasmid a genetic marker (cloning by retrieval) from the Escherichia coli chromosome or a co-electroporated DNA fragment. Additional protocols describe methods to screen for unselected mutations, removal of the defective prophage from recombineering strains, and other useful techniques.

/pdf/recombineering-genetic-engineering-in-bacteria-using-4n26lrv6vc.pdf

Recombineering: Genetic Engineering in Bacteria Using Homologous Recombination

Mini-λ: a tractable system for chromosome and BAC engineering

The bacterial chromosome and plasmids can be engineered in vivo by homologous recombination using PCR products and synthetic oligonucleotides as substrates. This is possible because bacteriophage-encoded recombination functions efficiently recombine sequences with homologies as short as 35 to 40 bases. This recombineering allows DNA sequences to be inserted or deleted without regard to location of restriction sites. This unit first describes preparation of electrocompetent cells expressing the recombineering functions and their transformation with double-stranded DNA (dsDNA) or single-stranded DNA (ssDNA). Support protocols describe a two-step method of making genetic alterations without leaving any unwanted changes, and a method for retrieving a genetic marker (cloning) from the E. coli chromosome or a coelectroporated DNA fragment and moving it onto a plasmid. A method is also given to screen for unselected mutations. Additional protocols describe removal of defective prophage, methods for recombineering.

UNIT 1.16 Recombineering: Genetic Engineering in Bacteria Using Homologous Recombination

Efficient expression of most bacteriophage λ early genes depends upon the formation of an antiterminating transcription complex to overcome transcription terminators in the early operons, pL and pR. Forma tion of this complex requires the phage-encoded protein N, the first gene product expressed from the pL operon. The N leader RNA contains, in this order: the NUTL site, an RNase III-sensitive hairpin and the N ribosome-binding site. N bound to NUTL RNA is part of both the antitermination complex and an autoregulatory complex that represses the translation of the N gene. In this study, we show that cleavage of the N leader by RNase III does not inhibit antitermination but prevents N-mediated translation repression of N gene expression. In fact, by preventing N autoregulation, RNase III activates N gene translation at least 200-fold. N-mediated translation repression is extremely sensitive to growth rate, reflecting the growth rate regulation of RNase III expression itself. Given N protein’s critical role in λ development, the level of RNase III activity therefore serves as an important sensor of physiological conditions for the bacteriophage.

/pdf/the-global-regulator-rnase-iii-modulates-translation-vtmz9vq641.pdf

The global regulator RNase III modulates translation repression by the transcription elongation factor N

One of the classical positive regulators of gene expression is bacteriophage lambda N protein. N regulates the transcription of early phage genes by participating in the formation of a highly processive, terminator-resistant transcription complex and thereby stimulates the expression of genes lying downstream of transcriptional terminators. Also included in this antiterminating transcription complex are an RNA site (NUT) and host proteins (Nus). Here we demonstrate that N has an additional, hitherto unknown regulatory role, as a repressor of the translation of its own gene. N-dependent repression does not occur when NUT is deleted, demonstrating that N-mediated antitermination and translational repression both require the same cis-acting site in the RNA. In addition, we have identified one nut and several host mutations that eliminate antitermination and not translational repression, suggesting the independence of these two N-mediated mechanisms. Finally, the position of nutL with respect to the gene whose expression is repressed is important.

/pdf/translational-repression-by-a-transcriptional-elongation-3k6l7skgk4.pdf

Helen R. Wilson

Papers

Recombineering: Genetic Engineering in Bacteria Using Homologous Recombination

Mini-λ: a tractable system for chromosome and BAC engineering

UNIT 1.16 Recombineering: Genetic Engineering in Bacteria Using Homologous Recombination

The global regulator RNase III modulates translation repression by the transcription elongation factor N

Translational repression by a transcriptional elongation factor.