In molecular biology, cytolethal distending toxin (cdt) is a toxin produced by Proteobacteria

Proteobacteria

The Proteobacteria are a major group of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera....

, including Escherichia coli

Escherichia coli

Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...

, Haemophilus

Haemophilus

Not to be confused with Haemophilia.Haemophilus is a genus of Gram-negative, pleomorphic, coccobacilli bacteria belonging to the Pasteurellaceae family. While Haemophilus bacteria are typically small coccobacilli, they are categorized as pleomorphic bacteria because of the wide range of shapes they...

spp and Campylobacter

Campylobacter

Campylobacter is a genus of bacteria that are Gram-negative, spiral, and microaerophilic. Motile, with either unipolar or bipolar flagella, the organisms have a characteristic spiral/corkscrew appearance and are oxidase-positive. Campylobacter jejuni is now recognized as one of the main causes...

spp.This toxin causes distension

Distension

Distension generally refers to an enlargement or ballooning effect:* Gastric distension - bloating of the stomach when air is pumped into it, as in a medical procedure* Abdominal distension - abdominal bloating, a symptom of several medical conditions...

 in certain cell lines, which eventually disintegrate and die. It consists of three subunits: A, B and C. Their sizes are approx. 27.7, 29.5 and 19.9kDa respectively, and they appear to be entirely novel. Further research on the complete toxin has revealed that it blocks the cell cycle

Cell cycle

The cell cycle, or cell-division cycle, is the series of events that takes place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission...

 at stage G2

G2 phase

G2 phase is the 3rd and final subphase of Interphase in the cell cycle directly preceding Mitosis. It follows the successful completion of S phase, during which the cell’s DNA is replicated...

, through inactivation of the cyclin-dependent kinase

Cyclin-dependent kinase

thumb|350px|Schematic of the cell cycle. outer ring: I=[[Interphase]], M=[[Mitosis]]; inner ring: M=Mitosis; G1=[[G1 phase|Gap phase 1]]; S=[[S phase|Synthesis]]; G2=[[G2 phase|Gap phase 2]]...

 Cdk1, and without induction of 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...

 breaks. This leads to multipolar abortive mitosis

Mitosis

Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...

 and micronucleation, associated with centrosomal

Centrosome

In cell biology, the centrosome is an organelle that serves as the main microtubule organizing center of the animal cell as well as a regulator of cell-cycle progression. It was discovered by Edouard Van Beneden in 1883...

 amplification. The roles of each subunit are unclear, but it is believed that they have separate roles in pathogenicity

Pathogenicity

Pathogenicity is the ability of a pathogen to produce an infectious disease in an organism.It is often used interchangeably with the term "virulence", although virulence is used more specifically to describe the relative degree of damage done by a pathogen, or the degree of pathogenicity caused by...

.