Involvement of p34cdc2 in establishing the dependency of S phase on mitosis

Mutants of cdc2+ can disrupt the dependency of S phase on completion of the previous mitosis. By changing the state of p34cdc2 it is possible to reprogramme a cell from entering mitosis to undergoing S phase. This leads to the proposal that the cell cycle can be considered a p34cdc2 cycle, and has implications for the evolution of life cycles.     

A recycling pathway between the endoplasmic reticulum and the Golgi apparatus for retention of unassembled MHC class I molecules

Assembly of class I major histocompatibility complex (MHC) molecules involves the interaction of two distinct polypeptides (the heavy and light chains) with peptide antigen. Cell lines synthesizing both chains but expressing low levels of MHC class I molecules on their surface as a result of a failure in assembly and transport have been identified. We now report that although the apparent steady-state distribution in these cells of class I molecules is in the endoplasmic reticulum (ER), the molecules in fact are recycled between the ER and Golgi, rather than retained in the ER. This explains the failure of class I molecules to negotiate the secretory pathway. Class I molecules do not seem to be modified by Golgi enzymes, suggesting that the proteins do not reach the Golgi apparatus during recycling. But morphological and subcellular fractionation evidence indicates that they pass through the cis Golgi or a Golgi-associated organelle, which we postulate to be the recycling organelle. This compartment, which we call the 'cis-Golgi network', would thereby be a sorting organelle that selects proteins for return to the ER.     

Induction of formation of presynaptic terminals in neuroblastoma cells by synapsin IIb

The synapsins are a family of closely related phosphoproteins (termed synapsins Ia, Ib, IIa and IIb) associated with synaptic vesicles and implicated in the short-term regulation of neurotransmitter release from nerve endings. During development, expression of the synapsins correlates temporally with synapse formation, but there has been no direct evidence that they are involved in synaptogenesis. Here we report that overexpression of synapsin IIb in the neuroblastoma x glioma hybrid clonal cell line NG108-15 leads, during cell differentiation, to marked increases in the number of neuritic varicosities and in the numbers of small clear vesicles and large dense core vesicles per varicosity, as well as to the appearance of synapse-like cell-cell contacts. Thus, synapsin IIb may be involved in the regulation of synapse formation and, as a result, in long-term neuronal signalling.     

A bayesian forecasting model for sequential bidding

In this paper we consider the problem facing a company in selecting the values of bids to submit on a sequence of contracts put out to tender. A simple-to-implement Bayesian forecasting model is presented, based on a steady Dirichlet process whose states are indexed by the possible bid decisions open to the company. The model gives an explicit algorithm for calculating the state probabilities, needing only data on the lowest bid made by the company's competitors. The flexibility of the basic model makes it a potentially powerful forecasting system for use by companies bidding for contracts.     

Presence of NAD pyrophosphorylase in skeletal muscle in dystrophic mice

Summary NAD pyrophosphorylase (ATP:NMN adenylyltransferase) activity has been measured in the skeletal muscle of dystrophic mice. The amount of this enzyme in the dystrophic mice, as determined by three different methods, was about one half of that in the controls. In addition, the concentration of ATP was too low to be detected in crude extracts of dystrophic mouse skeletal muscle, which were prepared using Tris buffer alone or Tris buffer containing either 3 M KCl, or 1 mM PMSF.     

A permutation-based algorithm for block clustering

Hartigan (1972) discusses the direct clustering of a matrix of data into homogeneous blocks. He introduces a stepwise divisive method for block clustering within a certain class of block structures which induce clustering trees for both row and column margins. While this class of structures is appealing, the stopping criterion for his method, which is based on asymptotic theory and the assumption that the individual elements of the data matrix are normally distributed, is quite restrictive. In this paper we propose a permutation-based algorithm for block clustering within the same class of block structures. By using permutation arguments to decide where to split and when to stop, our algorithm becomes applicable in a wide variety of cases, including matrices of categorical data and matrices of small-to-moderate size. In addition, our algorithm offers considerable flexibility in how block homogeneity is defined. The algorithm is studied in a series of simulation experiments on matrices of known structure, and illustrated in examples drawn from the fields of taxonomy, political science, and data architecture.     

Secretion and mechanism of action of the hole-forming toxin aerolysin

Aeromonas hydrophila exports aerolysin as a protoxin which is activated by proteolysis after release. Aerolysin binds to the eucaryotic cell receptor glycophorin and oligomerizes, forming holes in the membrane. Important regions of the molecule have been identified by site-directed mutagenesis, and channel formation has been studied in planar lipid bilayers.