Expression, gene

Assessing gene expression in vivo has been performed by magnetic resonance imaging and spectroscopy and briefly reviewed.  

Certain phthalate plasticizers such as di-(2-etltylhexyl) phthalate, DEHP, belong to the peroxisome prohferator, PP, family of rodent liver carcinogens. Here, the evidence for peroxisome proliferator-mediated rodent carcinogenesis in response to PPs will be considered together with an evaluation of the molecular basis for rodent-human species differences in response. Specifically, this chapter will focus on the role and mechanisms of peroxisome proliferator-induced rodent peroxisomal gene expression and the evidence for lack of relevance of this mechanism to humans. 

Nucleic acid hybridization allows scientists to compare and analyze DNA and RNA molecules of identical or related sequences. In a hybridization experiment, the experimenter allows DNA or RNA 

What happens if two nucleic acids are partly complementary and partly different In this case, some stretches of the two strands may form base pairs while others don t. The two molecules can be manipulated so that they form a hybrid or separate. The conditions favoring the formation of duplex nucleic acid are low temperature (below the Tm), high salt, and the absence of organic solvents. The latter two conditions raise the Tm of the hybrid duplex so that the DNA would remain more double-stranded. On the other hand, higher temperatures (closer to the Tm of the hybrid) lower salt, and the presence of organic solvents would tend to push the two strands of the DNA apart. 

High stringency (low salt, high temperature) Associated DNAs can have few mismatches. 

Hybridization can be used to classify the DNAs of various organisms. For example, human DNA is 98 percent identical to that of chimpanzees, and these two DNAs form a duplex under stringent conditions. Related sequences of humans and birds can also form hybrids, but only at a much lower stringency. 

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For the bioinformatician the emphasis lies on how a gene expresses a protein -an enzyme - that catalyzes a biochemical reaction (Figure 10.3-13). 

EST Expressed sequence tag. An EST is a partial sequence (typically less than 40C bases) selected from cDNA and used to identify genes expressed in a particuh tissue... 

Transcription First step in gene expression, corresponding to the generation of mRNA from the original DNA... 

Translation Second step in gene expression, the synthesis of proteins from mRNA... 

Genes are DNA and carry the inheritable characteristics of an organism and these characteristics are normally expressed at the molecular level via protein synthesis Gene expression consists of two stages transcription and translation, both of which involve RNAs Sections 28 11 and 28 12 describe these RNAs and their roles m transcription and translation... 

Section 28 11 Three RNAs are involved m gene expression In the transcription phase a strand of messenger RNA (mRNA) is synthesized from a DNA tern plate The four bases A G C and U taken three at a time generate 64 possible combinations called codons These 64 codons comprise the genetic code and code for the 20 ammo acids found m proteins plus start and stop signals The mRNA sequence is translated into a prescribed protein sequence at the ribosomes There small polynucleotides called... 

Transactivation. Protein synthesis is initiated or inhibited by the action of the activated GR on DNA. The use of glucocorticoids leads to antiinflammatory effects by first controlling gene expression, which subsequentiy leads to the synthesis and/or suppression of inflammation regulatory proteins. 

DNA sequence information is the starting poiat for other appHcations, including the expression of a gene product, the search for related sequences ia biological samples, in vitro mutageaesis of the sequeace, and stmcture—function studies of gene expression. 

The methods involved in the production of proteins in microbes are those of gene expression. Several plasmids for expression of proteins having affinity tails at the C- or N-terminus of the protein have been developed. These tails are usefiil in the isolation of recombinant proteins. Most of these vectors are commercially available along with the reagents that are necessary for protein purification. A majority of recombinant proteins that have been attempted have been produced in E. Coli (1). In most cases these recombinant proteins formed aggregates resulting in the formation of inclusion bodies. These inclusion bodies must be denatured and refolded to obtain active protein, and the affinity tails are usefiil in the purification of the protein. Some of the methods described herein involve identification of functional domains in proteins (see also Protein engineering). 

Gene Expression Systems. One of the potentials of genetic engineering of microbes is production of large amounts of recombinant proteias (12,13). This is not a trivial task. Each proteia is unique and the stabiUty of the proteia varies depending on the host. Thus it is not feasible to have a single omnipotent microbial host for the production of all recombinant proteias. Rather, several microbial hosts have to be studied. Expression vectors have to be tailored to the microbe of choice. 

Methods in Enymology 185 (1990). The entire volume covers gene expression. 

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