Insights Blog
-- Browse All Articles --
Physics Articles
Physics Tutorials
Physics Guides
Physics FAQ
Math Articles
Math Tutorials
Math Guides
Math FAQ
Education Articles
Education Guides
Bio/Chem Articles
Technology Guides
Computer Science Tutorials
Forums
Chemistry
Biology and Medical
Earth Sciences
Computer Science
Computing and Technology
DIY Projects
Trending
Featured Threads
Log in
Register
What's new
Search
Search
Search titles only
By:
Chemistry
Biology and Medical
Earth Sciences
Computer Science
Computing and Technology
DIY Projects
Menu
Log in
Register
Navigation
More options
Contact us
Close Menu
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Forums
Other Sciences
Biology and Medical
What is alpha-complementation?
Reply to thread
Message
[QUOTE="TytoAlba95, post: 6045775, member: 647883"] I am completely stumped by this question. I can't understand what is meant by complementation. Here's an excerpt from Primrose: [I]'The activity of the enzyme b-galactosidase is easily monitored by including in the growth medium the chromogenic substrate 5-bromo- 4-chloro-3-indolyl-b-D-galactoside (Xgal). This compound is colorless but on cleavage releases a blue indolyl derivative. On solid medium, colonies that are expressing active b-galactosidase are blue in color while those without the activity are white in color. This is often referred to as blue/white screening. Since Xgal is not an inducer of b-galactosidase, the non-substrate (gratuitous) inducer isopropyl-b-D-thiogalactoside (IPTG) is also added to the medium. The phenomenon of a-complementation of b-galactosidase is widely used in molecular genetics. The starting-point for a complementation is the M15 mutant of E. coli. This has a deletion of residues 11–41 in the lacZ gene and shows no b-galactosidase activity. Enzyme activity can be restored to the mutant enzyme in vitro by adding a cyanogen bromide peptide derived from amino acid residues 3–92 (Langley et al. 1975, Langley & Zabin 1976). Complementation can also be shown in vivo. I[B]f a plasmid carrying the N-terminal fragment of the lacZ gene encompassing the missing region is introduced into the M15 mutant, then [U]b-galactosidase is produced (how?)[/U][/B], as demonstrated by the production of a blue color on medium containing Xgal. In practice, the plasmid usually carries the lacI gene and the first 146 codons of the lacZ gene, because in the early days of genetic engineering this was a convenient fragment of DNA to manipulate. Since wild-type b-galactosidase has 1021 amino acids, it is encoded by a gene 3.1 kb in length. While a gene of this length is easily manipulated in vitro, there are practical disadvantages to using the whole gene. As will be seen later, it is preferable to keep cloning vectors and their inserts as small as possible. The phenomenon of a-complementation allows genetic engineers to take advantage of the lac system without having to have the entire Z gene on the vector.'[/I] [/QUOTE]
Insert quotes…
Post reply
Forums
Other Sciences
Biology and Medical
What is alpha-complementation?
Back
Top