MICROBIOLOGY

The Expressions of Mutation:  The expression of a mutation will only be readily noticed if it produces a detectable, altered phenotype. A mutation from the most prevalent gene form, the wild type, to a mutant form is called a forward mutation. Later, a second mutation may make the mutant appear to be a wild-type organism again. Such a mutation is called a reversion mutation because the organism seems to have reverted back to its original phenotype. A true back mutation converts the mutant nucleotide sequence back to the wild-type sequence. The wild-type phenotype also can be regained by a second mutation in a different gene, a suppressor mutation, which overcomes the effect of the first mutation.  If the second mutation is within the same gene, the change may be called a second site reversion or intragenic suppression. Thus, although revertant phenotypes appear to be wild types, the original DNA sequence may not be restored. In practice, a mutation is visibly...

MUTATION :  Considerable information is embedded in the precise order of nucleotides in DNA. For life to exist with stability, it is essential that the nucleotide sequence of genes is not disturbed to any great extent. However, sequence changes do occur and often result in altered phenotypes. These changes are largely detrimental but are important in generating new variability and contribute to the process of evolution. Microbial mutation rates also can be increased, and these genetic changes have been put to many important uses in the laboratory and industry. Mutations [Latin mutare, to change] were initially characterized as altered phenotypes or phenotypic expressions. Long before the existence of direct proof that a mutation is a stable, heritable change in the nucleotide sequence of DNA, geneticists predicted that several basic types of transmitted mutations could exist. They believed that mutations could arise from the alteration of single pairs of nucleotide...

M E D I C I N E:  Epigenetics, Nucleosome Structure, and Histone Variants Information that is passed from one generation to the next— to daughter cells at cell division or from parent to offspring—but is not encoded in DNA sequences is referred to as epigenetic information. Much of it is in the form of covalent modification of histones and/or the placement of histone variants in chromosomes. The chromatin regions where active gene expression (transcription) is occurring tend to be partially decondensed and are called euchromatin. In these regions, histones H3 and H2A are often replaced by the histone variants H3.3 and H2AZ, respectively. Shown here are the core histones and a few of the known variants. Sites of Lys /Arg residue methylation and Ser phosphorylation are indicated. HFD denotes the histone-fold domain, a structural domain common to all core histones chaperones, helping to ensure the proper assembly and placement of nucleosomes. Histone H3.3 dif...

CURING DISEASE BY INHIBITING TOPOISOMERASE : The topological state of cellular DNA is intimately connected with its function. Without topoisomerases, cells cannot replicate or package their DNA, or express their genes—and they die. Inhibitors of topoisomerases have therefore become important pharmaceutical agents, targeted at infectious agents and malignant cells. Two classes of bacterial topoisomerase inhibitors have been developed as antibiotics. The coumarins, including novobiocin and coumermycin A1, are natural products derived from Streptomyces species . They inhibit the ATP binding of the bacterial type II topoisomerases, DNA gyrase and topoisomerase IV. These antibiotics are not often used to treat infections in humans, but research continues to identify clinically effective variants. The quinolone antibiotics, also inhibitors of bacterial DNA gyrase and topoisomerase IV, first appeared in 1962 with the introduction of nalidixic acid. This compound had ...

Bacteria In cancer Therapy ( On Humble Request from  Maria Alejandra Cano Cháves ) Source:  http://www.jbiomedsci.com/content/17/1/21 Abstract: Resistance to conventional anticancer therapies in patients with advanced solid tumors has prompted the need of alternative cancer therapies. Moreover, the success of novel cancer therapies depends on their selectivity for cancer cells with limited toxicity to normal tissues. Several decades after Coley's work a variety of natural and genetically modified non-pathogenic bacterial species are being explored as potential antitumor agents, either to provide direct tumoricidal effects or to deliver tumoricidal molecules. Live, attenuated or genetically modified non-pathogenic bacterial species are capable of multiplying selectively in tumors and inhibiting their growth. Due to their selectivity for tumor tissues, these bacteria and their spores also serve as ideal vectors for delivering therapeutic proteins to tumors. Bacterial toxin...