REGULATION OF GENE EXPRESSION

             Gene expression is also controlled by environmental signals. In prokaryotes, nutrient availability is one of the most important environmental signals in controlling transcription, e.g., lactose acts as transcription inducer of the enzymes responsible for its digestion. In eukaryotes the cell’s hence they live in less variable environmental signal in controlling transcription, e.g., lactose acts as transcription inducer of the enzymes responsible for its digestion. In eukaryotes the cell’s immediate environmental factors which control gene expression are light and temperature. Light induces production of ribulose 1.5 biphosphate (RuBP) carboxylase, plays an important role in photosynthesis, in plants, similarly at high temperature the cell produces a group of proteins that help to stabilize internal cellular environment. These proteins are formed in both prokaryotesand eukaryotes and are called heat-shock proteins.

 

      Most frequently, eukaryotic gene expression is induced by hormones, growth factor and other related compounds. These are called signal molecules, as they convey signals within and between cells of a multicellurar organism, inducing changes in gene expression. Two of the major classes of hormones which control gene expression are: peptide and steroid hormones.

 

     With the molecular understanding of inheritance, an explosion of research became possible. One important development was the chain termination DNA sequencing in 1977 by Federick Sanger. With the help of this technology scientists were able to read then nucleotide sequence of a DNA molecule. Through the pooled efforts of the Human Genome Project and the parallel private efforts by Celera Genomics, the sequencing of human genome was possible (see Animal World Chapter 5 Human Genetics).  Another landmark in the history of molecular genetics is the discovery of restriction enzymes. The very basis of all genetic engineering and biotechnology and manipulation gene is possible because these basic understanding of DNA, the molecule of life.