Cotransformation
Encyclopedia
Cotransformation is the simultaneous transformation
of two or more genes
.
Only genes in the same chromosomal vicinity can be transformed; the closer together the genes lie, the more frequently they will be cotransformed. By contrast, genes sufficiently far apart that they cannot appear together on a fragment of donor
DNA
will almost never be cotransformed, because transformation is so inefficient that recipient cells usually take up only a single DNA.
, investigators isolated B. subtilis bacteria
with two mutations—trpC2 and hisB2—that made them Trp- , His- auxotrophs. These double auxotrophs served as the recipient in the study, wild-type cells (Trp+ , His+ ) were the donors. In this study, the numbers of Trp+ and His+ transformants were equal. Further tests showed that 40 of every 100 Trp+ transferred colonies were also His+. Similarly, tests of the His+ transformants showed that roughly 40% are also Trp+ . Thus, in 40% of the analyzed colonies, the trpC+ and hisB+ genes had been cotransformed.
, why are the two B.subtilis genes cotransformed with such high frequency? Because the trpC and hisB genes lie very close together on the chromosome and are thus genetically linked. Although the donor chromosome is fragmented into small pieces of about 20 kb during its extraction for the transformation process, the wild-type trpC+ and hisB+ alleles are so close that they often appear in the same donor DNA molecule
. Sequence analysis
shows that trpC and hisB genes are only about 7 kb apart.
Transformation
-Mathematics:* Transformation * Transformation * Integral transform* Data transformation * Transformation matrix-Natural science:* Phase transformation, a physical transition from one medium to another...
of two or more genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
.
Only genes in the same chromosomal vicinity can be transformed; the closer together the genes lie, the more frequently they will be cotransformed. By contrast, genes sufficiently far apart that they cannot appear together on a fragment of donor
Donor
A donor in general is a person who donates something voluntarily. Usually used to represent a form of pure altruism but sometimes used when the payment for a service is recognised by all parties as representing less than the value of the donation and that the motivation is altruistic...
DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
will almost never be cotransformed, because transformation is so inefficient that recipient cells usually take up only a single DNA.
Example
In one study of natural transformationNatural transformation
In category theory, a branch of mathematics, a natural transformation provides a way of transforming one functor into another while respecting the internal structure of the categories involved. Hence, a natural transformation can be considered to be a "morphism of functors". Indeed this intuition...
, investigators isolated B. subtilis bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
with two mutations—trpC2 and hisB2—that made them Trp- , His- auxotrophs. These double auxotrophs served as the recipient in the study, wild-type cells (Trp+ , His+ ) were the donors. In this study, the numbers of Trp+ and His+ transformants were equal. Further tests showed that 40 of every 100 Trp+ transferred colonies were also His+. Similarly, tests of the His+ transformants showed that roughly 40% are also Trp+ . Thus, in 40% of the analyzed colonies, the trpC+ and hisB+ genes had been cotransformed.
Explanation
Since during transformation, donor DNA replaces only a small percentage of the recipient’s chromosomeChromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
, why are the two B.subtilis genes cotransformed with such high frequency? Because the trpC and hisB genes lie very close together on the chromosome and are thus genetically linked. Although the donor chromosome is fragmented into small pieces of about 20 kb during its extraction for the transformation process, the wild-type trpC+ and hisB+ alleles are so close that they often appear in the same donor DNA molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
. Sequence analysis
Sequence analysis
In bioinformatics, the term sequence analysis refers to the process of subjecting a DNA, RNA or peptide sequence to any of a wide range of analytical methods to understand its features, function, structure, or evolution. Methodologies used include sequence alignment, searches against biological...
shows that trpC and hisB genes are only about 7 kb apart.