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  Section: General Biochemistry » Nucleic Acid Synthesis
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Regulation of Transcription in Bacteria

Content of Nucleic Acid Synthesis
» Nucleic Acids
» Structure and Function of Nucleic Acids
    » Basic Chemical Structure
    » Base Pairing in Nucleic Acids: Double Helical Structure of Dna
    » Size, Structure, Organization, and Complexity of Genomes
    » Information Storage, Processing, and Transfer
    » Chromosomal Dna Compaction and Its Implications in Replication and Transcription
    » DNA Sequence and Chromosome Organization
    » Repetitive Sequences: Selfish DNA
    » Chromatin Remodeling and Histone Acetylation
» Nucleic Acid Syntheses
    » Similarity of DNA and RNA Synthesis
    » DNA Replication Vs Transcription: Enzymatic Processes
    » Multiplicity of DNA and RNA Polymerases
» DNA Replication and Its Regulation
    » DNA Replication
    » Regulation of DNA Replication
    » Regulation of Bacterial DNA Replication at the Level of Initiation
    » DNA Chain Elongation and Termination in Prokaryotes
    » General Features of Eukaryotic DNA Replication
    » Licensing of Eukaryotic Genome Replication
    » Fidelity of DNA Replication
    » Replication of Telomeres—The End Game
    » Telomere Shortening: Linkage Between Telomere Length and Limited Life Span
» Maintenance of Genome Integrity
» DNA Manipulations and their Applications
» Transcriptional Processes
    » Recognition of Prokaryotic Promoters and Role of S-Factors
    » Regulation of Transcription in Bacteria
    » Eukaryotic Transcription
    » RNA Splicing in Metazoans
    » Regulation of Transcription in Eukaryotes
    » Fidelity of Transcription (RNA Editing)
» Chemical Synthesis of Nucleic Acids (Oligonucleotides)
» Bibliography of Nucleic Acid Synthesis
Unlike replication of the complete genome, which is essential for cellular propagation, not all genes need to be transcribed in a particular cell for its survival. Synthesis of mRNA is required for generation of proteins. Because not all proteins are required at all times for cellular survival and metabolism, both in prokaryotes and eukaryotes, and many proteins are expressed only in specific stages of development and differentiation in higher eukaryotes, a gene’s transcription is often highly regulated. Furthermore, the stability ofmRNAs and the proteins they encode vary over a wide range. Thus, different mRNAs are not made at the same rate. Additionally, the bulk of RNA, and in fact a large fraction of the cell mass, consists of ribosomal and transfer RNAs needed for carrying out protein synthesis. Both ribosomal and transfer RNAs are extremely stable.

Regulation of transcription, first investigated in bacterial viruses, primarily in E. coli, an intestinal microbe and its bacteriophage λ, is the foundation of molecular genetics. The ease of generating and manipulating mutants of various genes in E. coli and λ led to the discovery of repressors, which are proteins that bind to operator sequences of genes and turn off transcription. The genes that were originally studied encode enzymes for sugar (lactose and galactose) metabolism. Inactivation of these genes and their expression could be studied because the proteins are not essential for bacterial survival. An activator needed for expression of lactose-metabolizing β-galactosidase was identified; it is downregulated in the presence of glucose (“glucose effect”) and upregulated by binding to 3´-5´ cyclic AMP.

Significant advances in elucidating the mechanism of transcriptional regulation came from the life cycle studies of the lysogenic λ virus, whose virus-specific proteins are not expressed in the lysogenic state, when its duplex DNA genome is linearly integrated in the host chromosome. Here again, both positive and negative regulatory mechanisms are in play to fine tune the expression of genes from a low maintenance level during lysogeny to large-scale expression of the viral genome when the lysogenic virus enters the lytic phase of growth and exploits the host cell synthetic machinery for replication of its own viral DNA, RNA, and proteins.

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