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Replication in Prokaryotes

Replication in Prokaryotes

Mismatch Repair

Mismatch Repair

DNA Topoisomerases

DNA Topoisomerases

Topoisomerases are enzymes that relax overwound DNA molecules during various cell processes, including DNA replication and transcription. These enzymes regulate positive and negative DNA supercoiling without changing the nucleotide sequence. DNA overwinding in a clockwise direction results in positively supercoiled DNA, whereas underwinding in a counterclockwise direction produces negatively supercoiled DNA.
Types and Mechanism of action
Topoisomerases are divided into two main types. Type I...

Replication in Prokaryotes

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DNA replication has three main steps: initiation, elongation, and termination. Replication in prokaryotes begins when initiator proteins bind to the single origin of replication (ori) on the cell's circular chromosome. Replication then proceeds around the entire circle of the chromosome in each direction from the two replication forks, resulting in two DNA molecules.
Many Proteins Work Together to Replicate the Chromosome
Replication is coordinated and carried out by a host of specialized...

Mismatch Repair

Mismatch Repair

Organisms are capable of detecting and fixing nucleotide mismatches that occur during DNA replication. This sophisticated process requires identifying the new strand and replacing the erroneous bases with correct nucleotides. Mismatch repair is coordinated by many proteins in both prokaryotes and eukaryotes.
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Bacterial pathogens depend on precise and efficient DNA replication to sustain infection. Two type II topoisomerases—DNA gyrase and topoisomerase IV—are critical to this process, as they resolve DNA supercoiling and unlink chromosomes during replication. Fluoroquinolones, synthetic derivatives of quinolones, exploit this mechanism by stabilizing the transient DNA–enzyme cleavage complex, preventing strand religation, and causing lethal double-strand breaks. These antibiotics are selectively...

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Inducing a Site Specific Replication Blockage in E. coli Using a Fluorescent Repressor Operator System

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Conformational changes in E. coli DNA topoisomerase I.

H Feinberg¹, C D Lima, A Mondragón

¹Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, 2153 Sheridan Road, Evanston, Illinois 60208, USA.

Nature Structural Biology

|October 3, 1999

Summary

DNA topoisomerases manage DNA topology by breaking and resealing DNA strands. A key 30 kDa fragment in E. coli DNA topoisomerase I undergoes significant conformational changes, facilitating DNA passage.

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Area of Science:

Molecular Biology
Enzymology
Structural Biology

Background:

DNA topoisomerases are essential enzymes that regulate DNA topology.
They function by creating transient breaks in the DNA backbone.
Conformational changes are hypothesized to be crucial for their catalytic mechanism.

Purpose of the Study:

To investigate the proposed conformational changes in Escherichia coli DNA topoisomerase I.
To elucidate the role of a specific 30 kDa fragment in the enzyme's reaction cycle.

Main Methods:

Structural analysis of the 30 kDa fragment of E. coli DNA topoisomerase I.
Examination of domain arrangement and conformational flexibility.

Main Results:

The 30 kDa fragment exhibits significant conformational flexibility.
This fragment consists of two domains whose relative arrangement can change substantially.
These conformational changes are proposed to create an entrance for DNA passage.

Conclusions:

The dynamic conformational changes of the 30 kDa fragment are critical for the function of E. coli DNA topoisomerase I.
Understanding these structural dynamics provides insight into DNA topology regulation.