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Harrington, Maureen A.; Jones, Peter A.
doi: 10.1002/bies.950080403pmid: 3288193
Mouse embryo cells, primed to differentiate with the hypomethylating agent 5‐azacytidine (5‐aza‐CR), provide an excellent model system in which cellular differentiation can be studied at the molecular level. An inherent advantage of this system is the availability of clonal populations of cells representative of the non‐differentiated precursor, those whose determinative state is that of a specific lineage, and the end stage, phenotypically mature cell. Analysis of these cultures at the cellular and molecular level will advance our understanding of requirements for and the mechanism of action of growth modulators as well as the necessity for controlled expression of certain proto‐oncogenes. At a more fundamental level, the system can be used to identify, isolate and characterize genes whose expression alters the phenotypic fate of cells.
Jeang, Kuan‐Teh; Khoury, George
doi: 10.1002/bies.950080404pmid: 2837174
Enhancer elements are short stretches of nucleotides operationally defined by their cis‐acting ability to increase the transcription of nearby genes. They function relatively independently of position, orientation, and distance. Some show narrow tissue specificity while others permit constitutive expression in many different cell types. Although the first enhancer was described for simian virus 40 (SV40) more than five years ago, its mechanism of action has remained unclear. This review describes some of the models proposed to explain the physical role of enhancers in eukaryotic transcription.
Mattia, Elena; van Renswoude, Jos
doi: 10.1002/bies.950080405pmid: 3288194
Iron delivered by transferrin to the interior of the cell is in part utilized in biosynthetic processes and in part incorporated into ferritin, the major iron storage protein. The intracellular ferritin concentration is directly correlated to and determined by the extent of iron supply to the cell. Intracellular partitioning of iron to ferritin is suggested as forming the basis of cellular iron homeostasis.
Higgins, Christopher F.; Gallagher, Maurice P.; Mimmack, Michael L.; Pearce, Stephen R.
doi: 10.1002/bies.950080406pmid: 3288195
A large number of cellular proteins bind ATP, frequently utilizing the free energy of ATP hydrolysis to drive specific biological reactions. Recently, a family of closely related ATP‐binding proteins has been identified, the members of which share considerable sequence identity. These proteins, from both prokaryotic and eukaryotic sources, presumably had a common evolutionary origin and include the product of the white locus of Drosophila, the P‐glycoprotein which confers multidrug resistance on mammalian tumours, and prokaryotic proteins associated with such diverse processes as membrane transport, cell division, nodulation and DNA repair. A comparison of these various proteins provides valuable insights into the function and evolution of the multicomponent systems with which they are associated.
Harrison, Lionel G.; Tan, Karen Y.
doi: 10.1002/bies.950080407pmid: 3132150
Two general features of metameric patterning in Drosophilaare considered: (1) maintenance of a constant number of metameres (segments or parasegments) in the face of variation in length of the embryo; (2) expression of pattern by on‐off switchings of particular genes, with only three or four rows of cells to each element of pattern. For each of these features, the general strategic question is raised: could reaction‐diffusion theory account for this? In both cases, it is answered affirmatively. For the second feature, this review contains some hitherto unpublished computer simulations by one of us (K. Y. T.), illustrating that a reaction‐diffusion mechanism can be transformed into a patterned switching mechanism by nothing more than compartmenting of the diffusion region. For the scale of three compartments to one pattern repeat unit (representing three rows of cells to a segment) the switching pattern predicted by computation is two‐off to one‐on. This resembles the pattern of expression of the engrailed gene, posteriorly localized in each segment.
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