ABSTRACT
Introduction.............................................................................................................. 73 6.1 The Gene ........................................................................................................ 74 6.2 Transcription: Basic Mechanism of mRNA Biogenesis ............................... 76 6.3 Regulation of Transcription ........................................................................... 80 6.4 Transcriptional Regulation through Signal Transduction ............................. 83 6.5 RNA Interference ........................................................................................... 85 6.6 Gene Silencing ............................................................................................... 86 6.7 Sources of Variation in Gene Expression...................................................... 87 6.8 Measuring Gene Expression .......................................................................... 88 References................................................................................................................ 92
Gene expression, or transcription, is an important element of “The Central Dogma,” the phrase used by Francis Crick1 to describe what was and still is thought to be the basic and only flow of genetic information in a cell: DNA is transcribed to messenger RNA (mRNA) which is then translated to protein. In this scheme, only nucleic acids actually contain information that is encoded in the specific sequence of nucleotides that make up the DNA or RNA. Cells can construct proteins from the information contained in nucleic acids, but the transfer of information is one way; cells do not have the capacity to reproduce nucleic acid sequence information from proteins alone. While it is known that RNA performs more than just information functions,2 proteins are still thought to be the primary working molecules in a cell carrying out diverse functions related to energy management, immune response, structure, transport and storage, signal transduction, cell division, etc. Thus, implicit in the Central Dogma are mechanisms for the tightly controlled regulation of mRNA and thus protein amount, one of several mechanisms through which the cell maintains strict control over the final activity of a protein. On a grander scale, the integrated transcriptional activity of the entire genome (the entire DNA sequence in an organism) to a great extent determines the nature of a cell and its interactions with other cells in an organism or with the environment.
