摘要:

AbstractThe replicon hypothesis, first proposed in 1963 by Jacob and Brenner(1), states that DNA replication is controlled at sites called origins. Replication origins have been well studied in prokaryotes. However, the study of eukaryotic chromosomal origins has lagged behind, because until recently there has been no method for reliably determining the identity and location of origins from eukaryotic chromosomes. Here, we review a technique we developed with the yeastSaccharomyces cerevisiaethat allows both the mapping of replication origins and an assessment of their activity. Two‐dimensional agarose gel electrophoresis and Southern hybridization with total genomic DNA are used to determine whether a particular restriction fragment acquires the branched structure diagnostic of replication initiation. The technique has been used to localize origins in yeast chromosomes and assess their initiation efficiency. In some cases, origin activation is dependent upon the surrounding context. The technique is also being applied to a variety of eukaryotic organism

ISSN:0265-9247    

DOI:10.1002/bies.950130702

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

年代:1991

数据来源: WILEY

摘要:

AbstractHydractinia echinatais a marine colonial hydroid, a relative of the more widely knownHydra. In contrast toHydra, embryogenesis, metamorphosis and colony growth inHydractiniaare experimentally accessible and therefore, provide an ideal model system for investigating the biochemical basis of pattern formation. In particular, the processes involved in the transformation of the drop‐shaped freely swimming larva into a sessile tube‐shaped polyp are easily monitored, because this transfomation can be induced by application of various substances. Our results indicate that the internal level of S‐adenosylmethionine (SAM), potentially the most important methyl donor in transmethylation processes, plays a key role in the onset of metamorphosis. It is also proposed that the internal level of SAM plays a pivotal role in the proportioning and spacing of polyps within the c

ISSN:0265-9247    

DOI:10.1002/bies.950130703

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

年代:1991

数据来源: WILEY

摘要:

AbstractAn increasing number of studies indicate that changes in cytosolic free Ca2+([Ca2+]c) mediate specific types of signal transduction in plant cells. Modulation of [Ca2+]cis likely to be achieved through changes in the activity of Ca2+channels, which catalyse passive influx of Ca2+to the cytosol from extracellular and intracellular compartments. Voltage‐sensitive Ca2+channels have been detected in the plasma membranes of algae, where they control membrane electrical properties and cell turgor. These channels are sensitive to 1,4‐dihydropyridines, which in animal cells specifically affect one class of voltage‐regulated plasma membrane Ca2+channel. Ca2+‐permeable channels with different pharmacological properties have been found in the plasma membrane of higher plants. Recent evidence suggests the existence of two discrete classes of Ca2+channel co‐resident in the vacuolar membrane (tonoplast) of higher plants. The first is gated by inositol 1,4,5‐trisphosphate, and bears a number of similarities to its animal counterpart which is located in the endoplasmic reticulum (ER). The second tonoplast Ca2+channel is voltage‐operated. However, the specific roles of these tonoplast channels in signal transduction have yet to

ISSN:0265-9247    

DOI:10.1002/bies.950130704

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

年代:1991

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950130705

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

年代:1991

数据来源: WILEY

摘要:

AbstractAlterations in the expression of certain genes or in their products can render benign tumor cells metastatic. Experimentally this has been quickly performed by transferring dominantly acting oncogenes such as c‐H‐rasEJinto susceptible cells, butin vivosuch a rapid qualitative change in a dominantly acting oncogene occurs only rarely, and progression to highly metastatic phenotypes is thought to occur through a slow stepwise process. Such slow changes can be reversible and need not involve known dominantly acting oncogenes, consistent with clinical observations. An important element of the natural progression of tumors to malignancy may be their ability to circumvent microenvironmental controls that regulate growth and cellular diversity and to evolve into heterogeneous phenotypes, a process that appears to involve mainly quantitative changes in gene expression but which can be rapidly stimulated in cell culture by the introduction of a dominantly acting oncogene. It is proposed that the highly malignant cells that have slowly evolvedin vivowith only a few qualitative gene changes have undergone extensive cycles of diversification and accumulation of quantitative changes in the expression of genes that encode products that are related to malignancy and metastasis. Thus, highly malignant cellular phenotypes can arise quickly through specific qualitative changes in critical controlling genes or more slowly by less critical qualitative genetic changes, coupled with cellular diversification and accumulation of quantitative changes in gene express

ISSN:0265-9247    

DOI:10.1002/bies.950130706

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

年代:1991

数据来源: WILEY

摘要:

AbstractInsect endoparasitoids are able to circumvent the defense reactions of their habitual hosts. In a hymenopteran wasp species, virus‐like particles, found on the egg surface are responsible for the protection against the encapsulation reaction of the host caterpillar. Some of the particle proteins are structurally and probably functionally related to host protein(s). Biological properties of some of the host proteins suggest that they might be involved in the insect defense reactio

ISSN:0265-9247    

DOI:10.1002/bies.950130707

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

年代:1991

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950130708

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

年代:1991

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950130709

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

年代:1991

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950130710

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

年代:1991

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950130711

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

年代:1991

数据来源: WILEY