PLASMIDOS PDF

DNA structure and architecture in the chromosome and plasmid of hyperthermophilic organisms, a theoretical approach. Hyperthermophilic organisms have been recognized as an important element in the origin and early evolution of life on Earth, but also as a model for exobiological studies. Analyzing their molecular dynamics can help us understand this important lifestyle. In this study, using bioinformatic tools, the DNA composition in chromosomes and plasmids of hyperthemophilic organism were compared, and their structure, probable amino acid bias and DNA flexibility were analyzed. In some chromosomes and plasmids shows differential features of DNA flexibility and skews in mutation rate, which suggests that only some molecular elements show high values of variability, contrary to the proposal of the flexible genome theory. Studies on extremophilic microorganisms have been a breakthrough for the fields of biochemistry Xu and Glansdorff, ; Conners et al.

Author:Fenrinos Meramar
Country:Finland
Language:English (Spanish)
Genre:Automotive
Published (Last):4 October 2009
Pages:328
PDF File Size:12.46 Mb
ePub File Size:18.54 Mb
ISBN:576-1-14641-607-8
Downloads:14103
Price:Free* [*Free Regsitration Required]
Uploader:Tojakus



Cohesive-end cloning is one of the most commonly employed techniques in molecular biology. Review these tips and tricks for cloning using restriction enzymes. Cloning of double-stranded DNA dsDNA molecules into plasmid vectors is one of the most commonly employed techniques in molecular biology. The procedure is used for sequencing, building libraries of DNA molecules, expressing coding and non-coding RNA, and many other applications. The purpose of this article is to discuss cohesive-end cloning—one method by which DNA fragments can be inserted into a plasmid vector using restriction digestion.

Future articles will discuss these. Restriction endonucleases recognize and cleave dsDNA at highly specific nucleotide sequences, or restriction sites. They are referred to as cohesive ends because of the hydrogen bond stabilization of the DNA bases that loosely holds the DNA ends together prior to ligation.

The specificity of restriction enzymes enables directional cloning, and the hydrogen bonding of cohesive ends increases the efficiency of cohesive-end ligation by as much as X over blunt-end ligation [1].

These features make cohesive-end cloning a highly useful method for molecular biology. Cohesive-end restriction cloning can be described in a relatively standard series of steps: First, the insert is designed with restriction sites that also occur in the vector multiple cloning site MCS , but not elsewhere in the insert or vector.

Second, the insert and plasmid are digested in separate reactions, using the chosen enzyme s. Following digestion, the plasmid is dephosphorylated, and both insert and plasmid are purified to remove all enzymes. In the remaining steps the insert is ligated into the plasmid, and the ligated plasmid is transformed into E. Below, the method is described in more detail with added tips that further increase its flexibility. Figure 1. A basic, directional cloning experiment. Additional nonspecific base pairs outside of the restriction enzyme recognition sites are included to provide for efficient restriction enzyme binding [1].

The blue lines indicate the cut sites. Hydrogen bonds stabilize this binding, making this method highly efficient.

A subsequent ligation reaction covalently links the insert to plasmid. Plasmids are one of the most common types of vectors used for amplifying and introducing DNA into cells. Plasmids are double-stranded, circular, extrachromosomal DNA molecules that contain the necessary DNA elements required for replication in E.

All plasmids must contain three basic features to be useful for cloning. A schematic drawing of a basic cloning vector is shown in Figure 2. The first required feature is the origin of replication, which recruits endogenous bacterial replication machinery to copy transformed plasmids. The number of copies of a plasmid produced within a single E. For example, pUC contains a high copy origin, producing — copies per cell under ideal conditions [1].

The endogenous E. The second is the MCS, which contains a number of closely spaced restriction enzyme recognition sequences that occur only in the MCS and can be used to insert one or more pieces of DNA in this region without disrupting the rest of the plasmid structure.

Third, plasmids must contain at least one antibiotic resistance gene. This enables the small percentage of bacteria that have taken up and copied the transfected plasmid to be selected using agar plates containing the specified antibiotic. In addition to these basic features, many commercial plasmids contain one or more features that facilitate cloning, regulate expression of experimental inserts, or add features to expressed RNA or proteins, making them one of the most versatile tools in molecular biology.

These added elements are almost always adjacent to the MCS. For most common applications, there is more than one appropriate vector choice so it is important to understand the features you need and to compare those with the advantages and disadvantages of the available vector tools. Figure 2. Key features of a plasmid. Three features are required for a plasmid. The plasmid vectors used for general cloning are usually 3—6 kb in length.

Check with the manufacturer of the plasmid for the recommended insert size range. In general, smaller inserts are easier to clone than larger ones. Longer sequences will also naturally contain more endogenous restriction sites than shorter inserts, limiting the enzymes that can be used for cloning without destroying the insert.

Several free online software programs are available to identify restriction sites within the plasmid and insert sequences, including Webcutter, RestrictionMapper, and NEBcutter. In some cases the MCS itself may need to be altered—e. Blunt-end cloning and the Gibson Isothermal Method are alternative methods to avoid this issue. In addition to providing efficient ligations, and the ability to clone directionally using double digests, another outcome of cohesive-end cloning is that ligation of the insert into the vector recreates the original restriction sites.

This can be useful for screening clones or for the addition of adjacent DNA sequences in a subsequent round of cloning. It is also important to note that most restriction enzymes will not cut a recognition sequence that is at, or very near, the end of the DNA.

Therefore, when selecting or engineering your restriction sites, it is important to include a few nonspecific bases, sometimes referred to as buffers, at the end of your insert. These allow the enzyme to bind the DNA efficiently prior to cleavage. Buffer length varies by enzyme and should be confirmed as part of the experimental design process. Also, avoid using restriction sites that are right next to each other in the MCS—a 12 bp buffer between cut sites is generally sufficient for most enzymes [1].

For the ligation to be effective, the restriction enzyme digestion must be stopped. Some enzymes are easily heat inactivated by incubation at high temperature for a short period of time. Others cannot be heat inactivated and digestion products have to be purified by column, gel, or phenol extraction methods prior to ligation.

Failure to inactivate restriction enzymes will create competing reactions, and produce little or no ligated DNA. Restriction enzyme reaction conditions are also very important.

Salt conditions that are too high or the presence of inhibitors can change the specificity of restriction enzymes. In some cases, this can result in nonspecific cutting, known as star activity, which will generate multiple fragments detected as multiple unexpected bands on a gel. The most common cause of star activity is evaporation of reaction buffer during long digestions, especially those conducted overnight. Perform overnight digestions in sufficient volumes and in small tubes that limit the surface area for evaporation or in a thermal cycler with a heated bonnet to prevent star activity.

If you are digesting with a single enzyme, or one that produces blunt ends, it is important to dephosphorylate the vector using an enzyme such as calf-intestinal alkaline phosphatase or shrimp alkaline phosphatase SAP. This prevents the vector from religating without incorporating the insert, which still has the requisite phosphates intact. If the ends of the vector can simply religate, the probability of two ends of the same molecule coming together is much higher than the correct ends of a separate vector and insert.

Do not dephosphorylate the insert. Gel purification of the vector removes any uncut vector that will generate background colonies on agar plates. It also removes restriction enzymes and the small DNA fragments cut from MCS that could religate if the vector is not dephosphorylated. Cohesive ends have an annealing temperature below room temperature because they are only a few bases long. Low temperature ligations help stabilize DNA interactions, but at the expense of enzyme activity.

The reduced activity of T4 ligase at lower temperatures can be partially compensated for by increasing the duration of the ligation reaction. In addition, because annealing temperature of the ends affects ligation efficiency, cohesive-end ligations with short or single base overhangs may benefit from higher concentrations of T4 ligase. For extended incubations, some researchers even add additional enzyme into the reaction midway through. Ligations are regularly carried out in the presence of excess insert.

For cohesive-end cloning, a relatively low insert:vector ratio of — should be effective but may need to be experimentally optimized. Formula 1 shows a simple method for calculating the amount of insert needed. Formula 1.

Calculation for the quantity of insert required for a given amount of plasmid. Organic solvents including ethanol and phenol are common laboratory reagents that can inhibit restriction enzymes. Bacteria also naturally inhibit cleavage at certain sites with endogenous Dam and Dcm methyltransferases. For these enzymes, grow the plasmid in commercially available E. Keeping glycerol stocks of plasmid-containing bacteria is an ideal means of storage.

Glycerol stocks preserve plasmid DNA and allow for quick production of additional plasmid. Fresh plasmid is produced by scraping the frozen glycerol stock with a sterile inoculating loop, and streaking a fresh agar plate containing the appropriate selection antibiotic. Find protocols for generating glycerol stocks in Sambrook and Russell [1].

Repeated freeze-thaw cycles will degrade nucleic acids, and should be avoided. Sambrook J and Russell DW, editors. Ready for gene construction, genome editing, PCR, or sequencing. Delivered purified and normalized. All rights reserved. For specific trademark and licensing information, see www. Chat now Submit question. Toggle navigation.

Order Menu. Cloning strategies, Part 2: Cohesive-end cloning. Print Page. Creating cohesive ends Restriction endonucleases recognize and cleave dsDNA at highly specific nucleotide sequences, or restriction sites. Sign up now. Gene fragments from to bp shipped plated, or in suspension and ready for use. Nuclease Decontamination Solution also available.

KORENI CELA KNJIGA PDF

Cloning strategies, Part 2: Cohesive-end cloning

Esto es un ejemplo de altruismo y como las colonias bacterianas se parecen a organismos multicelulares. Ha sido sugerido que M. Un experimento donde cinco sistemas toxina-antitoxina fueron eliminados de una cepa de E. El sistema tipo I toxina-antitoxina se produce por un mecanismo de ARN de interferencia. Los sistemas tipo I algunas veces incluyen un tercer componente. Los sistemas tipo II toxina-antitoxina son generalmente mejor entendidos que el tipo I. De Wikipedia, la enciclopedia libre.

PRINCIPIOS BASICOS Y CALCULOS EN INGENIERIA QUIMICA HIMMELBLAU PDF

Sistema toxina-antitoxina

.

Related Articles