E chromosome

The simplest and most sensitive assays for detecting clastogenic (i.e. chromosomal breaking) effects involve the use of mammalian cells. Cultures of established cell lines (e.g. Chinese hamster ovary) as well as primary cell cultures (e.g. human l)nnphocyte) may be used. After exposure to a range of chemical concentrations in the presence and absence of an appropriate metabolic activation system, the cell cultures are treated with a spindle inhibitor (e.g. vinblastine) to accumulate cells in a metaphaselike stage of mitosis. Cells are harvested at appropriate times and chromosome preparations are made, stained with DNA-specific dye and the metaphase cells are analysed under the microscope for chromosome abnormalities. 

The exact cause of schizophrenia has been the subject of extensive research. It appears that genetic factors (i.e., chromosomal abnormalities that cause deviations in brain structure and function) are the primary risk factors in the majority of people with schizophrenia (70% to 80%).15,23 Environmental factors (social stresses, prenatal or childhood brain injury, and so forth) seem to be the underlying cause in the remaining 20% to 30% of people with schizophrenia.23 The precise role of these factors, and the interplay between genetic and environmental factors, continues to be elucidated.28,50 61... 

Xu GL, Bestor TH, Bourch his D, Hsieh CL, Tommerup N, Bugge M, Hulten M, Qu X, Russo JJ, Yiegas-Pequignot E. Chromosome instability and immunodeficiency syndrome caused by mutations in a DNA methyltransferase gene. Nature 1999 402 187-191. 

CHIOU, C.H., MILLER, M., WILSON, D.L., TRAIL, F., LINZ, J.E., Chromosomal loeation plays a role in regulation of aflatoxin gene expression in A.spergillus parasiticus, Appl. Environ. Microbiol, 2002,68,306-315. 

There are a number of different reasons why non-DNA linkers have been considered necessary to hold DNA molecules in tandem arrangement in chromosomes. The most relevant of these to the regulation of DNA synthesis are as follows the presumption that replication units of DNA within a sin e chromosome cannot be directly connected to one another without interruption of the DNA double helix the need for a mechanism to relieve torsion of the DNA molecule, torsion developed in connection with semiconservative replication. The latter proposal that non-DNA linkers mi t serve to allow rotation of the DNA double helix during semiconservative replication is no longer considered valid since it has been repeatedly demonstrated that a single-stranded break in a DNA double helix allows the intact chain to serve as a swivel and release torsion within the molecule (Vlnograd and Lebowitz, 1966). 

Edstrom, J.E. Chromosomal RNA and other nuclear RNA fractions. In The role of chromosomes in development (Locke, M., ed.), p. 137-152. New York Academic Press 1964... 

Genes are segments of chromosomes. Some of the genes are coded to give each animate species its characteristics (e.g., color and number of eyes, type of hair, muscle), and others are coded to produce the chemicals required for the organism to live (metabolism). 

A number of studies have shown that vitamins moderate the induction of chromosomal aberrations by radiation. Vitamins C and E given orally to mice either 2 h before, immediately after, or 2 h after 1 Gy (100 rad) of y-ray TBI significantly reduce the frequencies of micronuclei and chromosomal aberrations in BM cells. Vitamin E is the more effective (95). Administration of vitamins C and E within 5 min of irradiation is as effective as pretreatment. Protection by vitamin C has also been shown in humans. Whereas chronic treatment of rats using vitamin C (100 or 300 mg/(kg/d)) for six months prior to TBI protects against chromosomal aberrations, vitamin E is not radioprotective in this setting (96). 

Because of the double helical nature of DNA molecules, their size can be represented in terms of the numbers of nucleotide base pairs they contain. For example, the E. coli chromosome consists of 4.64 X 10 base pairs (abbreviated bp) or 4.64 X 10 kilobase pairs (kbp). DNA is a threadlike molecule. The diameter of the DNA double helix is only 2 nm, but the length of the DNA molecule forming the E. coli chromosome is over 1.6 X 10 nm (1.6 mm). Because the long dimension of an E. coli cell is only 2000 nm (0.002 mm), its chromosome must be highly folded. Because of their long, threadlike nature, DNA molecules are easily sheared into shorter fragments during isolation procedures, and it is difficult to obtain intact chromosomes even from the simple cells of prokaryotes. 

To achieve overproduction of phenylalanine, the micro-organism should be derepressed at the pheA level and free of inhibition at the arcG level. Both genes are located on the chromosomal DNA of the micro-organism and, by means of amino add analogues such as p-fluoro-DL-phenylalanine, it is possible to make (phenylalanine) feedback resistant mutants of E.cdi (pheA and oroF mutants). The following procedure can be used ... 

---