摘要:

AbstractA recent study(1)of sequence data from many different proteins has suggested that contemporary prokaryotes and eukaryotes may have shared a common ancestor as recently as 2 billion years ago (the molecular clock). Strong evidence from the geological record, however, indicates that oxygen‐producing microorganisms, perhaps similar to modern cyanobacteria, existed 3.5 billion years ago. The fossil evidence, therefore, suggests that any common ancestor of prokaryotes and eukaryotes must have existed at least 1.5 billion years earlier than suggested by the molecular clock evidence. The discrepancy between molecular and geological evidence for the age of modern cells is considered here, as are aspects of gene descent in the tree of life that might help to account for i

ISSN:0265-9247    

DOI:10.1002/bies.950180702

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

年代:1996

数据来源: WILEY

摘要:

AbstractRho, a member of the Ras superfamily of small GTPases, has multiple biological roles: it regulates signal trasduction pathways linking extracellular growth factors to the assembly of actin stress fibres and focal adhesion complexes; it is required for G1progression and activates the SRF transcription factor when quiescent fibroblasts are stimulated to grow; and it plays a role later in the cell cycle during cytokinesis. Two groups have recently succeeded in identifying downstream effectors of Rho that may mediate some of these biological effects. One protein identified by both groups is protein kinase N (PKN), a serine/threonine kinase whose catalytic domain is closely related to that of protein kinase C(1,2).

ISSN:0265-9247    

DOI:10.1002/bies.950180703

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

年代:1996

数据来源: WILEY

摘要:

AbstractPlant cells are caged within a distended polymeric network (the cell wall), which enlarges by a process of stress relaxation and slippage (creep) of the polysaccharides that make up the load‐bearing network of the wall. Protein mediators of wall creep have recently been isolated and characterized. These proteins, called expansins, appear to disrupt the noncovalent adhesion of matrix polysaccharides to cellulose microfibrils, thereby permitting turgor‐driven wall enlargement. Expansin activity is specifically expressed in the growing tissues of dicotyledons and monocotyledons. Sequence analysis of cDNAs indicates that expansins are novel proteins, without previously known functional motifs. Comparison of expansin cDNAs from cucumber, pea,Arabidopsisand rice shows that the proteins are highly conserved in size and amino acid sequence. Phylogenetic analysis of expansin sequences suggests that this multigene family diverged before the evolution of angiosperms. Speculation is presented about the role of this gene family in plant development and evolut

ISSN:0265-9247    

DOI:10.1002/bies.950180704

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe purpose of this review is to draw attention to the mechanism of dosage compensation inDrosophilaas a model for the study of the regulation of gene activity through the modulation of transcription. Dosage compensation resembles some mechanisms of transcriptional regulation, found in widely divergent organisms, that do not play a role in the activation of silent genes but determine the level of activity of genes that have been induced through the action of specific activators. It differs from other known regulatory mechanisms in that its effect is to achieve, on average, a twofold change in gene activity levels. This review introduces the notion that, in order to yield such a defined level of regulation, the mechanism of dosage compensation inDrosophila, and perhaps inCaenorhabditisas well, incorporates elements that govern both transcriptional enhancement and repression within the same multi‐protein regulatory comple

ISSN:0265-9247    

DOI:10.1002/bies.950180705

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

年代:1996

数据来源: WILEY

摘要:

AbstractIn many cells, a nitric oxide (NO) synthase inducible by immunological stimuli produces a sustained flow of NO that lasts a long time. NO is a short‐lived molecule but it is a diffusibel ligand believed to be capable of reaching distal target sites. Further, several lines of evidence indicate that cysteine‐rich motifs of metal‐binding proteins, as well as redox‐sensitive metal clusters of metalloproteins, are natural sensors of bioradicals like NO. In metalloregulatory proteins, metals are often conveniently located at binding sites and bound to cysteine residues. Accordingly, disruption of the metal‐thiolate polymetallic clusters should trigger significant remodelling of the protein structure involved in regulation. We can therefore postulate that the nitrosation reaction occurring at metal centres or cysteine‐rich motifs will preclude correct binding to regulatory sites. Several examples are given of metalloregulatory proteins whose metal is bound to thiols and may then become sensitive to NO. Recent observations indicate that in response to NO synthesis, iron regulatory protein, a eukaryotic bifunctional [Fe‐S] protein, switches from acting as aconitase to being an RNA‐binding regulator, and we suggest that the interplay between NO or a NO‐derived molecule and metal clusters at critical allosteric sites may be a crucial component of the cellular response to env

ISSN:0265-9247    

DOI:10.1002/bies.950180706

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

年代:1996

数据来源: WILEY

摘要:

AbstractThree approaches have been used to investigate the inhibitory role of the cytokinin class of phytohormones in plant senescence: external application of cytokinins, measurement of endogenous cytokinin levels before and during senescence, and manipulation of endogenous cytokinin production in transgenic plants. In transgenic plant studies, endogenous cytokinin levels are manipulated by expression ofIPT, a gene encoding isopentenyl transferase. Transgenic plants expressingIPTfrom a variety of promoters exhibit developmental and morphological alterations and often display retarded leaf senescence. A recently developed autoregulatory senescence‐inhibition system targets cytokinin production quantitatively, spatially and temporally, and results in transgenic plants that exhibit significantly delayed senescence without abnormalities. These transgenic studies not only confirm the regulatory role of cytokinins in plant senescence, but also provide a way to manipulate senescence for potential agricultural application

ISSN:0265-9247    

DOI:10.1002/bies.950180707

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

年代:1996

数据来源: WILEY

摘要:

AbstractSignal transduction pathways constructed around a core module of three consecutive protein kinases, the most distal being a member of the extracellular signal‐regulated kinase (ERK) family, are ubiquitous among eukaryotes. Recent work has defined two cascades activated preferentially by the inflammatory cytokines TNF‐α and IL‐1‐β, as well as by a wide variety of cellular stresses such as UV and ionizing radiation, hyperosmolarity, heat stress, oxidative stress, etc. One pathway converges on the ERK subfamily known as the ‘stress activated’ protein kinases (SAPKs, also termed Jun N‐terminal kinases, JNKs), whereas the second pathway recruits the p38 kinases. Upstream inputs are diverse, and include small GTPases (primarily Rac and Cdc42; secondarily Ras) acting through mammalian homologs of the yeast Ste20 kinase, other kinase subfamilies (e.g. GC kinase) and ceramide, a putative second messenger for certain TNF‐α actions. These two cascades signal cell cycle delay, cellular repair or apoptosis in most cells, as well as activation of immune and reticul

ISSN:0265-9247    

DOI:10.1002/bies.950180708

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe autosomal recessive genetic disease, Fanconi anaemia, is perceived as another manifestation of defective cellular DNA repair, just as in the autosomal recessive disease Xeroderma pigmentosum. The biochemistry and cellular biology of Xeroderma pigmentosum have been convincingly elucidated, but the same has not been true for Fanconi anaemia. In this review we consider the pleiotropic nature of Fanconi anaemia, its clinical and cellular variability and its genetic heterogeneity. We take into account the wealth of experimental findings available and offer a novel hypothesis involving feedback control of DNA replication during S phase of the cell cycle to explain the basic defect in the disease.

ISSN:0265-9247    

DOI:10.1002/bies.950180709

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

年代:1996

数据来源: WILEY

摘要:

AbstractEvidence for recombination suppression has been identified in linkage studies of several unstable DNA diseases. Also sex‐specific changes in recombination frequency have been detected at the loci of Huntington's disease and myotonic dystrophy. It can be hypothesized that meiotic recombination is regulated by genome‐wide genomic imprinting and that changes in meiotic recombination imply the presence of the genomic imprinting defect. If aberrant recombination at the locus of trinucleotide repeat expansion is verified, new theoretical and experimental opportunities will arise in studies on the role of genomic imprinting in the unstable DNA disea

ISSN:0265-9247    

DOI:10.1002/bies.950180710

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

年代:1996

数据来源: WILEY

摘要:

AbstractRecent findings suggest thatC. elegans, albeit displaying an invariant cell lineage for embryonic development, uses the same basic strategy for embryogenesis as other organisms. The early embryo is regionalised by cell‐cell interaction

ISSN:0265-9247    

DOI:10.1002/bies.950180711

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

年代:1996

数据来源: WILEY