Regulation of Gene Expression A Variety of Mechanisms in Eukaryotes | Genetics, Biotechnology, Molecular Biology, Botany

⇒	Regulation of Gene Expression 3. A Variety of Mechanisms in Eukaryotes
⇒	Regulation at Transcription Level
	⇒	Activation of transcription
	⇒	Britten-Davidson model for unit of transcription
	⇒	Gene battery
	⇒	Chromosomal proteins and gene expression
⇒	Repression of transcription
	⇒	Specific DNA sequences controlling transcription
	⇒	Transgenic plants to study regulatory sequences
	⇒	Modification of DNA sequences and their transcripts in gene expression
	⇒	Alternative splicing of transcripts
⇒	Regulation at translation level
	⇒	Activation and repression of translation
	⇒	Masked mRNA in eggs of sea urchin and Xenopus
⇒	Regulation by gene re-arrangement
	⇒	Expression of immunoglobulin genes
	⇒	Yeast mating type switching
	⇒	Trypanosome surface antigen (VSG) switching
	⇒	Synthesis of mRNA in pieces in VSG genes in trypanosome
⇒	Regulation by reversible phosphorylation
⇒	Signal transduction and second messengers
	⇒	Proteins and peptide hormones and gene expression
	⇒	Steroid hormones and gene expression
	⇒	Interferon stimulated gene expression (without a second messenger)
	⇒	Cell surface receptors in cholesterol metabolism and drug production
	⇒	Ubiquitin protein and regulation of heat shock genes

During the last two decades, considerable information has become available on the regulation of gene expression in eukaryotes, although in the 1960's only bacteria were considered suitable for such studies. Due to inherent difficulties in working with multicellular eukaryotes, initial studies in these systems were restricted to the following : (i) formulation of theoretical models for the regulation of gene expression and (ii) conducting experiments to identify whether histones or non-histone chromosomal proteins are relatively more important for the regulation of the activity of specific genes in time and space (i.e. at specific developmental stage and in specific tissue). More recently (particularly after 1980), regulation of specific genes has been examined in greater detail giving valuable information. Specific DNA sequences and proteins (e.g. transcription factors) involved in regulation of specific genes have been identified. These specific genes express either in specialized cells or respond to specific stimuli and are variously described as luxury genes or smart genes as opposed to house keeping genes, which are constitutive in their expression.

A large number of transcription factors have been identified which take part in the formation of a transcription complex, which activates the enzyme, RNA polymerase and associated proteins to initiate transcription. Specific regulatory DNA sequences have also been identified (sometimes through the use of transgenic plants), which respond to stimuli and provide sites for binding of transcription factors. For transmission of stimuli (external or internal) to the target DNA sites, specific signal transduction pathways (involving intermediate receptor molecules) have been worked out in detail in many cases. Examples are also available now, where regulation of gene expression in eukaryotes is exercised at the post-transcriptional level involving RNA processing or translation. A remarkable phenomenon of regulation through genome reorganization or gene rearrangement has also been discovered in (i) human immune system involving antibody production, (ii) yeast mating types involving production of pheromones-receptors and in (iii) trypanosome's variable surface antigen-glycoprotein (VSG) production. All these aspects will be briefly described in this section.


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