[Sign in] [Register]   

EIAab logo

Index > News Center > News list.
Enter your KeyWord (Ex. ELISA Kit, Cuticular Active Peptide Factor, etc)
Search content in infomation.

The E coli initiator protein—DnaA, has four functional domains

Posted by star on 2018-08-20 23:24:03

    A great deal is known about the E. coli initiator protein, DnaA, even though its high resolution structure has not yet been determined. Considerable structure-function information has been obtained from biochemical studies and sequence comparisons with other proteins. Based on this information, the DnaA protein can be divided into four functional domains, which are numbered I to IV starting at the amino terminus.

    Each domain plays a critical role in the initiation of DNA synthesis. Domain I participates in DnaA oligomerization and also helps to recruit the DnaB protein, a helicase containing six identical subunits that is required to unwind the double helix so that DNA synthesis can be initiated. Domain ∏binds the Dna8 helicase transiently. Domain Ⅲ binds ATP or ADP and has an ATPase activity. The DnaA · ATP complex is essential for replication initiation. Domain IV binds to the replicator and helps to unwind the double helix so that the DnaB can be loaded onto the single strands that are generated. It also contains a membrane binding site that interacts with anionic glycerophospholipids in the cell membrane. This interaction facilitates the conversion of the DnaA · ADP complex to the DnaA · ATP complex, an essential step that must take place before a new round of replication can begin.

DNA replicator

Posted by star on 2018-08-20 01:37:04

    The replicon model proposes that a site-specific DNA-binding protein binds to a DNA sequence called a replicator.

    Although genes replicate as part of larger chromosomes, most cannot replicate as independent units. An independently replicating DNA molecule such as a viral, bacterial or eukaryotic chromosome or a plasmid that can maintain a stable presence in a cell is called a replicon.

    In the early 1960s Francois Jacob and Sydney Brenner proposed the replicon model to explain how DNA molecules replicate autonomously. The replicon model requires two specific components, an initiator protein and a replicator. The initiator protein binds to the replicator, a specific set of sequences within the DNA molecule that is to be replicated. Because the replicator must be part of the DNA that is to be replicated, it is said to be cis-acting. Once bound to the replicator the initiator helps to unwind the DNA and recruit components of the replication machinery. The specific site within the replicator at which replication initiated is called the origin of replication. Bacterial cells usually require just one origin of replication, which in E. coli is called oriC. Because a bacterial replicator is usually quite short (200 to 300 bp), the terms replicator and origin of replication tend to be used interchangeably even though technically the origin of replication is just a part of the replicator. Eukaryotes, which have much longer chromosomes than bacteria, require many origins of replication.

    Molecular biologists have learned a great deal about the replication process by studying mutants with blocks in specific steps in replication. E.coli and the proteins that they encode along with some information about the proteins. Because a defect in DNA synthesis would be lethal, most of the replication mutants that have been studied are temperature-sensitive. Early replication mutants were isolated before the functions of the altered genes were known, and therefore were named dnaA, dnaB, and so forth. A major reason for the gaps in the alphabetical listing is that some genes were renamed when they were later shown to influence DNA synthesis indirectly rather than directly. For instance, the gene originally named dnaF was renamed nrdA when it was shown to be the structural gene for a subunit in ribonucleoside diphosphate reductase, the enzyme that converts ribonucleotides to deoxyribonucleotides.

    Important clues to replication gene function were obtained by determining the effects that temperature shifts have on DNA synthesis in conditional mutants. A mutant with a defect in an enzyme required for chain extension will stop DNA synthesis immediately after being switched from a permissive to a restrictive temperature. For this reason they are called quick-stop mutants. In contrast, a mutant with a defect in an enzyme required for the initiation of DNA replication will complete the ongoing round of DNA synthesis but will not initiate a new round. These mutants are called slow-stop mutants because they continue to synthesize DNA for some time after the temperature switch. As more was learned about the replication process and additional mutants were discovered investigators named the new genes according to their function. For instance, gyrA and gyrB, the structural genes for the two subunits in DNA gyrase, were named for their function. We will now turn our attention to the initiation stage of the replication process.

    It is expected to become a new accurate tumor diagnosis method when near-infrared fluorescence imaging technology is applied to multiple detection in-vivo. The research which was proposed by Zhang fan, professor of chemistry of Fudan University, was published on August 6 in Nature Nanotechnology.

    At present, tissue biopsy has been the main method of diagnosis in clinical medicine. However, there are many risks and hidden dangers. So, it is urgent to find a new technology in the future that allows accurate diagnosis of tumors without surgical biopsy.

    Fluorescence imaging not only has the features of real-time and high spatial resolution, but also can be used to realize simultaneous multi-channel detection of multiple objects under test through multiple fluorescence signals of different wavelengths.

    However, when this imaging technology is used in the actual application of multiple imaging in vivo, people is often not satisfactory with the result. So Zhang Fan's team proposed the method of multiple imaging based on time dimension and realized multiple imaging in vivo by using the rare earth nanometer probe fluorescence signal with fluorescence emission in the second window area of near infrared.

    Compared with the traditional clinical diagnostic techniques by which only one tumor marker can be detected at a time, the time-dimensional imaging method proposed by Zhang Fan's team can quantify multiple tumor markers simultaneously, which significantly improves the detection efficiency. At the same time, the time dimension imaging method which is expected to become a new method for noninvasive cancer diagnosis can not only avoid the risk of metastatic tumor cell directly but also reduce the artificial misjudgment risk caused by traditional method in the process of tissue section, processing and evaluation.

    While the in vivo experiments described above provide considerable information about bacterial DNA replication, they do not shed much light on the cellular apparatus responsible for DNA replication. The best way to learn about the replication apparatus is to isolate it and then examine how each part works by itself and in concert with the other parts. This approach has been used to study the replication apparatus of viruses, bacteria, eukaryotes, and the archaea. Because the E. coli replication apparatus is probably the one that has been most thoroughly investigated, we begin by examining it. It is important to note that lessons learned from studying the E. coli replication apparatus appear to apply to the replication apparatus of other organisms.

    The replication apparatus is made of many different protein components that must be assembled on DNA before replication can begin. The first stage of DNA replication, initiation, involves the assembly of the replication apparatus at a unique site on the bacterial chromosome. Special proteins help to assemble the replication apparatus but do not participate further in the replication process. Initiation is followed by elongation, a process in which the leading strand is synthesized continuously and the lagging strand is synthesized discontinuously. A complex replication machine known as DNA polymerase Ⅲ holoenzyme is responsible for DNA synthesis during this stage. We will examine this replication machine in some detail. The final stage of replication, termination, begins when the two-replication forks meet about half way around the DNA molecule it also requires specific proteins.

Page 1 of 85
Hot Genes
ALCAM ACE KSR2 ASPRO C19orf80 Gdf5 Trap1a Atf2
Top Searches
Ubiquitin ELISA Ubiquitin-protein ligase metalloproteinase Asprosin TRAP1A Tumor necrosis vitamin d
Why choose EIAAB
Our products have been quoted by many publications in famous journals such as Cell; Cell Metabolism; Hepatology; Biomaterials.more
Further Information
About us Protein center Bank account Distributors Terms & Conditions Career

Copyright & copy www.eiaab.com2006-2016 All Rights Reserved    EIAab