Consruction of Tri-Plasmid Based Vectors Using Tuber Specific Gene Promoters from the Indian Potato Cultivars

Abstract

Regulation of gene expression is a vital process in the cell and involves the action of a host of specific protein factors, which can act at different steps in the gene expression pathway. This includes studies on the structure and regulation of the molecular machinery responsible for replication and transcription of DNA, the processing of RNA and the functional organization of chromatin, as well as studies on how genes and the factors acting on them are organized within the nucleus. Recombinant DNA technology allows us to manipulate the very DNA of living organisms and to make conscious changes in that DNA. The ability of a gene to produce a biologically active protein is much more complex in eukaryotes than in prokaryotes. A major difference is the presence in eukaryotes of a nuclear membrane, which prevents the simultaneous transcription and translation that occurs in prokaryotes. Whereas, in prokaryotes, control of transcriptional initiation is the major point of regulation, in eukaryotes the regulation of gene expression is controlled nearly equivalently from many different points. In eukaryotes, genomic DNA is packaged into chromosomes and kept in the cell nucleus, where genes are regulated and expressed. During each cell division cycle, the chromosomal DNA must be replicated exactly once, during S-phase, and then one copy of each replicated chromosome segregated into the two daughter cells during mitosis. When genes are expressed, the chromosomal DNA must be transcribed into RNA and the RNA then processed and transported to where it is needed. If left to the molecular machinery of a cell without control, the transcription apparatus of the cell would express every gene in the genome at once: unwinding the DNA double helix, transcribing each gene into single-stranded mRNA and, finally, translating the mRNA into protein. But, no cell can function amid the resulting cacophony. So, there exists a mechanism by which cells muzzle many genes, so that, at a given point of time, only a fraction, about 15% of the genes are expressed. This phenomenon is known as "Regulation of Gene Expression". There is another aspect to the control of gene expression in a cell, especially in eukaryotic cells and multicellular organisms. Each cell of a multicellular organism is "differentiated", i.e. it is specialized for a particular function. These cells are remarkably diverse, e.g. nerve cells, kidney cells, macrophages, myocytes, hair cells, etc. Some are short and fat; some are long and thin; some have appendages; and others are roughly spherical. Yet all of these cells contain the same set of genes. So, how do we explain their highly diverse phenotypes? The answer lies in the regulation of gene expression, and it plays an important role in development and differentiation. Study of regulation of gene expression is one of the thrust areas of modern molecular biology and biochemistry.