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doi: 10.1002/bies.950080502pmid: N/A
doi: 10.1002/bies.950080503pmid: 3044355
Until quite recently, recombinant DNA technology was not able to deal with DNA molecules larger than 20–40 kb. This is a serious limitation for the study of mammalian, and in particular human genomes whose total length is approx. 3 × 106 kb, since the best resolution of genetic and chromosomal analysis is usually the rough equivalent of 1000–5000 kb. Three recently developed methods promise to bridge this gap: pulsed field gel electrophoresis, which can analyze megabase‐sized DNA fragments; cloning in yeast, which can clone and propagate DNA fragments of several hundred kb; and jumping libraries, which allow ‘jumping’ over large distances along the chromosome. This review presents the current status of these very promising technologies.
doi: 10.1002/bies.950080504pmid: 3044356
Early embryogenesis of Caenorhabditis elegans provides a striking example of the generation of polarity and the partitioning of cytoplasmic factors according to this polarity. Microfilaments (MFs) appear to play a critical role in these processes. By visualizing the distribution of MFs and by studying the consequences of disrupting MFs for short, defined periods during zygote development, we have generated some new ideas about when and how microfilaments function in the zygote.
doi: 10.1002/bies.950080505pmid: 2841922
Our potential for dissecting the complex processes involved in eukaryotic DNA replication has been dramatically increased with the recent development of cell‐free systems that recreate many of these processes in vitro. Initial results from these systems have drawn together work on the cell cycle, the enzymology of replication, and the structure of the nucleus.
Gilbert, Lawrence I.; Combest, Wendell L.; Smith, Wendy A.; Meller, Victoria H.; Rountree, Dorothy B.
doi: 10.1002/bies.950080506pmid: 3044357
Insect molting is elicited by a class of polyhydroxylated steroids, ecdysteroids, that originate in the prothoracic glands. Ecdysteroid synthesis in the prothoracic glands is controlled in large measure by a peptide hormone from the brain, prothoracicotropic hormone (PTTH), which exists in two forms and is released into the general circulation as a result of environmental and developmental cues. The means by which PTTH activates the prothoracic glands has been examined at the cellular level and the data reveal the involvement of cAMP, calcium, calmodulin, cAMP‐dependent protein kinase and the ultimate phosphorylation of a 34 kDa protein tentatively identified as ribosomal protein S6.
doi: 10.1002/bies.950080507pmid: 3044358
The unfertilized sea urchin egg is a metabolically quiescent cell. Fertilization results in the activation of a variety of metabolic and biosynthetic pathways, including a 20‐ to 40‐fold increase in the rate of protein synthesis by 2 h after fertilization. This increase is regulated at a purely translational level without the need for new transcription. The greatest part of this increase is due to the translation of stored maternal mRNAs which were not translated in the egg. There is also a 2‐to 3‐fold increase in the peptide elongation rate. The molecular and physiological mechanisms responsible for this activation process are beginning to be understood, and turn out to be much more complex than was anticipated.
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