摘要:

AbstractThe first complete sequence of an archaebacterial genome, that ofMethanococcus jannaschii, has recently been published(1). Less than half of the open reading frames (ORFs) can be assigned a function based on similarity to known sequences in databases. These assignable ORFs fall into two general classes; those involved in transcription, translation and replication are more similar to eukaryotic homologs, while those determining metabolic processes are more similar to eubacterial versions. The immense but very rewarding task of making biological and evolutionary sense of all this information has only just begun.

ISSN:0265-9247    

DOI:10.1002/bies.950190102

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

年代:1997

数据来源: WILEY

摘要:

AbstractCiliated protozoa have separate germline and somatic nuclei, yet unlike larger organisms, both nuclei reside in the same cytoplasm. The micronuclei contain the germline and the macronucleus is the somatic nucleus. Thousands of DNA elements are normally removed from the micronuclear genome as it forms a new macronucleus during each sexual cycle. A recent study directly links the excision of these internal eliminated sequences (IESs) to mating type determination by showing that a pleiotropic mutation affecting mating type also prevents the excision of an IES from a surface protein gene(1). Remarkably, once the IES is present in the old macronucleus it prevents excision of that specific IES during formation of the next macronucleus.

ISSN:0265-9247    

DOI:10.1002/bies.950190103

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

年代:1997

数据来源: WILEY

摘要:

AbstractA recent article by Galitski and Roth(1)characterizes adaptive reversion of chromosomallac−mutations inSalmonella typhimuriumLT2. Using a classical genetic approach they show that adaptive reversion, as characterized by the appearance of late revertant colonies, is an exception rather than a general phenomenon for reversion of nonsense, missense, frameshift and insertion mutations. For certain mutations, however, the number of late revertants exceeds the predicted number. These excess revertants suggest that adaptive mutability is applicable to chromosomal genes as well as to genetic changes involving F plasmids and lysogenic phage

ISSN:0265-9247    

DOI:10.1002/bies.950190104

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

年代:1997

数据来源: WILEY

摘要:

AbstractMos, a protein kinase, is specifically expressed and functions during meiotic maturation (or G2/M progression) of vertebrate oocytes. When expressed ectopically, however, it can also readily induce oncogenic transformation (or uncontrolled G1/S transitions) in somatic cells. In both of these cell types, Mos activates mitogen‐activated protein kinase (MAPK), which seems largely to mediate its different functions in both oocyte maturation and cellular transformation. In oocyte maturation, the Mos‐MAPK pathway probably serves to activate and stabilize M‐phase promoting factor (MPF) (possibly by inhibiting some negative regulator(s) of this factor), while in cellular transformation, it seems to stabilize and activate the nuclear oncoprotein c‐Fos as well as to induce transcription of its gene. Thus, the different functions of Mos in oocytes and somatic cells may arise chiefly from its different MAPK‐mediated targets in the respective cell types. This review discusses the cellular basis that may enable Mos to act differently in oocytes and soma

ISSN:0265-9247    

DOI:10.1002/bies.950190105

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

年代:1997

数据来源: WILEY

摘要:

AbstractOne distinguishing feature of vertebrate oocyte meiosis is its discontinuity; oocytes are released from their prophase I arrest, usually by hormonal stimulation, only to again halt at metaphase II, where they await fertilization. The product of the c‐mosproto‐oncogene, Mos, is a key regulator of this maturation process. Mos is a serine‐threonine kinase that activates and/or stabilizes maturation‐promoting factor (MPF), the master cell cycle switch, through a pathway that involves the mitogen‐activated protein kinase (MAPK) cascade. Oocytes arrested at prophase I lack detectable levels of Mos, which must be synthesized from a pool of maternal mRNAs for proper maturation. While Mos is necessary throughout maturation inXenopus, it seems to be required only for meiosis II in the mouse. The translational activation of c‐mosmRNA at specific times during meiosis requires cytoplasmic polyadenylation.Cis‐andtrans‐acting factors for polyadenylation are, therefore, essential element

ISSN:0265-9247    

DOI:10.1002/bies.950190106

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

年代:1997

数据来源: WILEY

摘要:

AbstractOocytes, eggs and blastomeres of the embryo are special cells that undergo rapid changes in structure and function at developmental transitions. These changes are frequently regulated by cytoplasmic signaling events, particularly at the developmental transition of fertilization, because the genome is largely inactivated at this time. Protein kinase C (PKC) is a signaling agent that acts after the sperm‐induced rise in calcium and has a central role in the remodeling of the structure of the egg into the zygote in many species. PKC also acts during other developmental transitions. This kinase serves as a chronometer, which can choreograph the cell's remodeling events in both space and time. Several technical advancements discussed in this review have permitted a better understanding of the actions of PK

ISSN:0265-9247    

DOI:10.1002/bies.950190107

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

年代:1997

数据来源: WILEY

摘要:

AbstractEver since it was discovered in hydra, regeneration has remained a stimulating question for developmental biologists. Cellular approaches have revealed that, within the first few hours of apical or basal hydra regeneration, differentiation and determination of nerve cells are the primary cellular events detectable. The head and foot activators (HA, FA), neuropeptides that are released upon injury, are signaling molecules involved in these processes. In conditions where it induces cellular differentiation or determination, HA behaves as an agonist of the cyclic AMP (cAMP) pathway involving the modulation of CREB nuclear transcription factor activity. This cascade would be required for proper regeneration, regardless of whether the polarity involved is apical or basal. Modulations of the protein kinase C pathway, which have been shown to affect apical or basal positional values, might signal to bring about this polarity; however, endogenous ligands responsible for this modulation are as yet unknown.

ISSN:0265-9247    

DOI:10.1002/bies.950190108

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

年代:1997

数据来源: WILEY

摘要:

AbstractIntegrins are ubiquitous trans‐membrane adhesion molecules that mediate the interaction of cells with the extracellular matrix (ECM). Integrins link cells to the ECM by interacting with the cell cytoskeleton. In cases such as leukocyte binding, integrins mediate cell‐cell interactions and cell‐ECM interactions. Recent research indicates that integrins also function as signal transduction receptors, triggering a number of intracellular signaling pathways that regulate cell behavior and development. A number of integrins are known to stimulate changes in intracellular calcium levels, resulting in integrin activation. Although changes in intracellular calcium regulate a vast number of cellular functions, this review will discuss the stimulation of calcium signaling by integrins and the role of intracellular calcium in the regulation of integrin‐mediated a

ISSN:0265-9247    

DOI:10.1002/bies.950190109

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

年代:1997

数据来源: WILEY

摘要:

AbstractPeroxisomes are eukaryotic organelles that are the subcellular location of important metabolic reactions. In humans, defects in the organelle's function are often lethal. Yet, relative to other organelles, little is known about how cells maintain and propagate peroxisomes or how they direct specific sets of newly synthesized proteins to these organelles (peroxisome biogenesis/assembly). In recent years, substantial progress has been made in elucidating aspects of peroxisome biogenesis and in identifying PEX genes whose products, peroxins, are essential for one or more of these processes. The most progress has been made in understanding the mechanism by which peroxisome matrix proteins are imported into the organelles. Signal sequences responsible for targeting proteins to the organelle have been defined. Potential signal receptor proteins, a receptor docking protein and other components of the import machinery have been identified, along with insights into how they operate. These studies indicate that multiple peroxisomal protein‐import mechanisms exist and that these mechanisms are novel, not simply variations of those described for other organelle

ISSN:0265-9247    

DOI:10.1002/bies.950190110

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

年代:1997

数据来源: WILEY

摘要:

AbstractImmunofluorescent labelling demonstrates that human metaphase chromosomes contain hyperacetylated histone H4. With the exception of the inactive X chromosome in female cells, where the bulk of histone H4 is under‐acetylated, H4 hyperacetylation is non‐uniformly distributed along the chromosomes and clustered in cytologically resolvable chromatin domains that correspond, in general, with the R‐bands of conventional staining. The strongest immunolabelling is often found in T‐bands, the subset of intense R‐bands having the highest GC content. The majority of mapped genes also occurs in R‐band regions, with the highest gene density in T‐bands. These observations are consistent with a model in which hyperacetylation of histone H4 marks the position of potentially active gene sequences on metaphase chromosomes. Since acetylation is maintained during mitosis, progeny cells receive an imprint of the histone H4 acetylation pattern that was present on the parental chromosomes before cell division. Histone acetylation could provide a mechanism for propagating cell memory, defined as the maintenance of committed states of gene expression through

ISSN:0265-9247    

DOI:10.1002/bies.950190111

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

年代:1997

数据来源: WILEY