DNA-Binding Proteins

DNA-Binding Proteins

Structural proteins that bind DNA are well-understood examples of non-specific DNA-protein interactions. Within chromosomes, DNA is held in complexes with structural proteins. These proteins organize the DNA into a compact structure called chromatin. In eukaryotes this structure involves DNA binding to a complex of small basic proteins called histones, while in prokaryotes multiple types of proteins are involved.The histones form a disk-shaped complex called a nucleosome, which contains two complete turns of double-stranded DNA wrapped around its surface. These non-specific interactions are formed through basic residues in the histones making ionic bonds to the acidic sugar-phosphate backbone of the DNA, and are therefore largely independent of the base sequence.Chemical modifications of these basic amino acid residues include methylation, phosphorylation and acetylation.These chemical changes alter the strength of the interaction between the DNA and the histones, making the DNA more or less accessible to transcription factors and changing the rate of transcription. Other non-specific DNA-binding proteins in chromatin include the high-mobility group proteins, which bind to bent or distorted DNA. These proteins are important in bending arrays of nucleosomes and arranging them into the larger structures that make up chromosomes.


A distinct group of DNA-binding proteins are the DNA-binding proteins that specifically bind single-stranded DNA. In humans, replication protein A is the best-understood member of this family and is used in processes where the double helix is separated, including DNA replication, recombination and DNA repair.These binding proteins seem to stabilize single-stranded DNA and protect it from forming stem-loops or being degraded by nucleases.
The lambda repressor helix-turn-helix transcription factor bound to its DNA target
In contrast, other proteins have evolved to bind to particular DNA sequences. The most intensively studied of these are the various transcription factors, which are proteins that regulate transcription. Each transcription factor binds to one particular set of DNA sequences and activates or inhibits the transcription of genes that have these sequences close to their promoters. The transcription factors do this in two ways. Firstly, they can bind the RNA polymerase responsible for transcription, either directly or through other mediator proteins; this locates the polymerase at the promoter and allows it to begin transcription. Alternatively, transcription factors can bind enzymes that modify the histones at the promoter; this will change the accessibility of the DNA template to the polymerase.


As these DNA targets can occur throughout an organism's genome, changes in the activity of one type of transcription factor can affect thousands of genes.Consequently, these proteins are often the targets of the signal transduction processes that control responses to environmental changes or cellular differentiation and development. The specificity of these transcription factors' interactions with DNA come from the proteins making multiple contacts to the edges of the DNA bases, allowing them to "read" the DNA sequence. Most of these base-interactions are made in the major groove, where the bases are most accessible

Ways of giving Chemotherapy

Ways of giving Chemotherapy

Depending on the type of cancer, chemotherapy can be administered orally or intravenously (directly into the vein).

* Chemotherapy Oral (swallowing tablets)

These are in the form of tablets. If the health of the patient allows, he / she is able to put them into the house. Nevertheless, regular visits to hospitals are still needed to check on the health of the patient and the response to treatment.

It is vital for making tablets directly at specified. If the t forget to take one patient at a given time he / she should call the medical staff immediately.

* Chemotherapy intravenous (directly into the vein)

Intravenous chemotherapy can be given as follows:

o The direct injection into a vein.
o By drip (intravenous infusion).
o Three or infusion pump.
o Three pumps the patient bears for several weeks or months. This is known as continuous infusion, venous infusion fadálach, or ambulatory infusion (the patient may progress during the reception of the medication resources).

There are several ways to medication in the patient. These include:

o cannula - a thin tube is inserted through the skin into the vein - usually the body that comes through the back of the hand or low hand.

o infusion (intravenous infusion) - in order to dilute the medication may be rare in the bag. The solution in the bag through a tube in the hands of patients and in the vein (intravenous infusion). Cannula will be used. The solution slowly into the vein.

Chemotherapy by pressure are generally dripping from the pump. Do not hurry the pumping of the process, instead causes the solution into the vein at constant speed in a given period - the slower the rate, the longer it will take the whole thing.

o Central line - this is a long, flexible plastic line (thin tube) to come into the center of blood vessels in the chest, near the heart. The central line is usually the body goes through the center of the chest under the skin and increases in large artery near the collarbone (clavicle). The only visible part of the length of a line from the date is a little hole in the chest.

o peripherally inserted central catheter (PICC) line - the long, thin, flexible tube that is required in a vein, usually in the arm and makes its way into a large vein in the fund is near the heart. It is like a central line, but has a different point of entry.

o portacath (implantable ports) - which, for thin soft, flexible plastic tube going into a vein. It is the port (opening) just under the skin of the fund or arm. The port on which thin rubber disc special needles to pass a medical, or taken from the blood.

Pregnancy and contraception
Many chemotherapy drugs can cause birth defects. It is important to prevent a pregnant woman chemotherapy. Since most chemotherapy drugs in oral contraceptives is important to use a barrier method of contraception such as condoms, during the entire period of chemotherapy treatment and for years after treatment completion. If you are pregnant, you should tell the medical staff immediately prior. If you fall pregnant during treatment immediately tell the medical staff.

Gene Mapping by In Situ Hybridization

Gene Mapping by In Situ Hybridization

The previous mapping methods are indirect in that they provide information on the physical location of a gene on a particular chromosome but without actually visualizing the gene's map position. A more direct approach is in situ hybridization, which involves hybridizing DNA (or RNA) probes directly to metaphase chromosomes spread on a slide and visualizing the hybridization signal (and thus the location of the gene to which the probe hybridizes) under a microscope.

The DNA in metaphase chromosomes is denatured in place (hence, in situ) on the slide, and hybridization of a labeled probe is allowed to proceed. Methods for mapping single-copy gene sequences by in situ hybridization originally were laborious and slow, requiring long exposures of the slides under photographic emulsion to detect the location of hybridized probe that had been labeled with low-level isotopes, such as tritium. Mapping with confidence required analysis of many metaphase spreads to distinguish the real hybridization signal from background radioactivity. However, more sensitive techniques have now been developed that enable rapid detection of hybridized probes labeled non radioactively with compounds that can be visualized by fluorescence microscopy (Fig). Even in a single metaphase spread, one can easily see the position of the gene being mapped.

In combination with banding methods for chromosome identification, fluorescence in situ hybridization can be used to map genes to within 1 to 2 million base pairs (1000 to 2000 kb) along a metaphase chromosome. Although this degree of resolution is a considerable improvement over other methods, it is still substantially larger than the size of most individual genes.


Figure: Gene mapping by in situ hybridization of a biotin-labeled DNA probe for the human muscle glycogen phosphorylase gene (MGP) to a spread of human metaphase chromosomes. Location of the MGP gene is indicated by the bright spots seen over each chromatid at the site of the gene in band q13 of chromosome 11. The mapping of MGP to 11q13 also assigns the locus for McArdle disease, an autosomal recessive myoglobinuria caused by deficiency of MGP. (Photograph courtesy of Peter Lichter, Yale University)

The deafness gene

The deafness gene


The mutation of MicroRNA mir-96 leads to progressive loss of hearing if present in single copy, and deafness if present in two copies

The journal Nature Genetics have posted the results of a search conducted under the projects "Sirocco" and "Eurohear", funded by the European Union. The discovery concerns the association between a new type of gene and the progressive loss of hearing, because the mir-96 gene is a small piece of RNA that affect the process of generation of other molecules in sensory hair cells of the inner ear .

The results come from the collaboration of two research groups, one Spanish and one English.

Karen Steel, one of the coordinators of the team of British Sanger Institute, said "We were able to demonstrate relatively quickly if the mice that were carriers of one copy of the variant of this gene suffer from progressive loss of hearing, and if they were carrying both genes, they were suffering from severe hearing loss. The principal questions to be answered concerning the possibility to determine which variant was involved and how influences on hearing "

Having identified the chromosome 7, the possible location of the gene altered the two groups of researchers have sequenced the gene in each "homologous genomic regions in man and mouse that are associated with hearing loss" and showed the presence of a mutation in the gene mir - 96.

Miguel Angel Moreno-Pelayo, author of the study and researcher at the Hospital Ramon y Cajal in Spain, said "We know a number of genes associated with deafness in humans and mice, but we discovered with surprise that this belongs to a new class of MicroRNA genes defined. No one had observed a mutation that can cause disease in a couple of MicroRNA sequence. This is the first MicroRNA gene associated with hearing loss and e 'is significant that the first to be associated with a hereditary condition. "

Experts recognize that the MicroRNA may bind to the active messengers in the generation of cell protein, effectively stopping the process and now have discovered that it is possible to analyze the role of mutation in mice. It seems the sensory hair cells in the mutant mice are affected by mir-96 gene, while mice carrying two copies of the gene mutant hair cells are deformed from birth and cells subjected to a degeneration in the early stages of life.

Morag Lewis of the Sanger Institute, who discovered the mutation, commented "The mutation, or variation of a single letter of genetic code from A to T in this tiny extension, is sufficient to cause a serious loss in mice" .

This mechanism also occurs in humans but, according to analysis of the two families used as a sample, the mutation does not happen ever in the same regions where the mouse, although affect neighboring regions, and always very important for the proper functioning of mir-96 .

Race for the Double Helix

Race for the Double Helix

The Watson-Crick model of DNA was a Nobel Prize winning structure. But what differed from this one to all of the other DNA structures that already existed? Well, Watson and Crick discovered the DNA was double-helical. Previously it was believed that DNA had a triple helix. Watson and Crick knew that the phosphates could not be located on the outside while the bases were on the inside.

The novel feature of their structure was that the two chains were held together by a purine and pyrimidine base. They are joined in pairs, a single base from one chain being hydrogen-bonded to a single base from the other chain, so that the two lie side by side with identical z-co-ordinates. Adenine (purine) is paired with thymine  (pyrimidine), and guanine (purine) is paired with cytosine (pyrimidine). Many times it will be written like: A-T, G-C.

As we already know, DNA consists of two strands, and each of those strands consist of a phosphate-sugar-phosphate backbone with bases (A, T, C or G) on the sugar molecules. The two strands run opposite of each other, with the bases pointing inwards and (as mentioned above) adenine is always paired with thymine, and guanine is always paired with cytosine. Therefore, if you know the sequence of one strand, then you know the sequence of the other strand. They are mirror images in reverse.