摘要:

AbstractMutations within theSteel and Dominant Spottingloci of mice have led to the recent identification of a growth factor/receptor system required for the normal development of germ cells, pigment cells and hematopoietic cells. Interactions between the products of these genes, Steel factor and c‐Kit respectively, have now been demonstrated to influence various developmental processes, including survival, proliferation, and/or differentiation of cells in a tissue specific manner. In addition, our current understanding of the molecular basis of variousSteelandDominant Spottingalleles coupled with the emerging information on the expression pattern ofsteel factorand c‐kittranscripts during development, is now beginning to explain the pleiotropic affects of these mutati

ISSN:0265-9247    

DOI:10.1002/bies.950150202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe expression of certain eukaryotic genes is – at least in part – controlled at the level of mRNA translation. The step of translational initiation represents the primary target for regulation. The regulation of the intracellular iron storage protein ferritin in response to iron levels provides a good example of translational control by a reversible RNA/protein interaction in the 5' untranslated region of an mRNA. We consider mechanisms by which mRNA/protein interactions may impede translation initiation and discuss recent data suggesting that the ferritin example may represent the ‘tip of the iceberg’ of a more general theme for translational

ISSN:0265-9247    

DOI:10.1002/bies.950150203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWntsare a recently described family of secreted glycoproteins related to theDrosophilasegment polarity gene,wingless, and to the proto‐oncogene,int‐1.Wntsare thought to function as developmental modulators, with signalling distances of only a few cell diameters. InXenopus, at least sixWnts, includingXwnts‐1, ‐3A, and ‐4, are expressed initially in the developing central nervous system, with some regions expressing multipleXwnts.Xwnt‐8 is expressed by mid‐blastula stage, in ventral and lateral mesoderm.Xwnt‐5A mRNAs are stored in the egg, and later are expressed throughout the embryo in both ectoderm and mesoderm, but with a pronounced enrichment in the head and tail. Recent studies inXenopushave pursued the diverse roles ofXwntsin early development, the mechanisms by whichXwntssignal information between cells, and the cell physiological response

ISSN:0265-9247    

DOI:10.1002/bies.950150204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractMany bacteria respond in a coordinate manner to environmental changes. External stimuli, sensed by receptors, are transduced to regulatory proteins which participate in well defined pathways of gene expression by varying their structure and mode of action. The network of environmental signal transduction is responsible for a fine and continuous communication between the host and the pathogenic bacteria. As a result, the gene expression machinery of the pathogen is modified continuously, in order to establish the optimal conditions for bacterial survival and multiplication.

ISSN:0265-9247    

DOI:10.1002/bies.950150205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractUrokinase and its receptor are essential components of the cell migration machinery, providing an inducible, transient and localized cell surface proteolytic activity. This activity has been shown to be required in normal and pathological forms of cellular invasiveness (i.e. in several embryonic developmental processes, during inflammatory responses and cancer metastasis and spreading). It represents one of the best known of the protcolytic systems which are currently under investigation in this field. The urokinase receptor allows a continuous regulation of the proteolytic activity at cell contacts, utilizing the different localization of urokinase and its inhibitors. The receptor, in fact, in addition to focusing the enzymatic activity at focal and cell‐cell contacts, also regulates it by internalizing and degrading only the inhibited form of urokinase. Internalized receptor releases the ligands to the lysosomes and recycles back to surface. In this way, the proteolytically active areas of the cell surface can be continuously monitored for their activity and their location modified. The cell can thus coordinate its migration efforts with a step‐wise modification of the proteolytic activity‐map of the cell surface. The urokinase cycle can be supported by one individual cell (autocrine) or by two or more cells. In the latter case, complementation and synergism of urokinase and its receptor are

ISSN:0265-9247    

DOI:10.1002/bies.950150206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractRNA processing inEscherichia coliand some of its phages is reviewed here, with primary emphasis on rRNA and tRNA processing. Three enzymes, RNase III, RNase E and RNase P are responsible for most of the primary endonucleolytic RNA processing events. The first two are proteins, while RNase P is a ribozyme. These three enzymes have unique functions and in their absence, the cleavage events they catalyze are not performed. On the other hand a relatively large number of exonucleases participate in the trimming of the 3′ ends of tRNA precursor molecules and they can substitute for each other. Primary processing is the first event that happens to the nascent RNA molecule, while in secondary RNA processing, the substrate is a product of a primary processing event. Although most RNA processing occurs in RNP particles, it seems that only in secondary RNA processing is the RNP particle required for the reaction. Bacteria and especially bacteriophages contain self‐splicing introns which in cases were probably acquired from other spec

ISSN:0265-9247    

DOI:10.1002/bies.950150207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe simian virus 40 chromosome, a model for the mammalian replicon, is a uniquely powerful system for the study of drugs and treatments which target enzymes of the mammalian replication apparatus. High resolution gel electrophoretic analysis of normal and aberrant viral replication intermediates can be used effectively to understand the molecular events of replication failure. These events include breakage of replication forks, aberrant topoisomerase action, failure to separate daughter chromosomes, protein‐DNA crosslinking, single and double strand DNA breakage, alterations in topology and inactivation of replication intermediates. The SV40 replication system can also be used to study the recombinational events which often follow drug‐induced replication fail

ISSN:0265-9247    

DOI:10.1002/bies.950150208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950150209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractCellular dedifferentiation is an important developmental response to perturbations in morphogenesis. In the cellular slime moldDictyostelium discoideumthis process gives cells the flexibility, when multicellular development is disrupted, to respond to nutrients and reinitiate vegetative growth. Recent studies inD. discoideumdescribed by Soll and colleagues(1)show that genes previously thought to be expressed only during spore germination are also expressed during induced dedifferentiation, suggesting that similar molecular mechanisms are involved in these two developmental processes. It should now be possible to determine whether the developmental programs that control dedifferentiation during spore germination also control conversion of cell types in the multicellular organism.

ISSN:0265-9247    

DOI:10.1002/bies.950150210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950150211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY