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The product of the FEN2 gene of Saccharomyces cerevisiae has previously been described as a protein conferring sensitivity to the antifungal agent fenpropimorph. Fen2p was postulated to act as a common regulator of carbon and nitrogen catabolite repression and of amino acid and ergosterol biosynthesis. In this paper, we present experimental evidence characterizing Fen2p as a plasma membrane-localized transporter for the vitamin pantothenate. The high affinity transport system (Km = 3.5 microM) is sensitive to uncouplers, suggesting a H+-pantothenate cotransport. Pantothenate transport rates in yeast are modulated by extracellular pantothenate, being maximal at low pantothenate concentrations. It is demonstrated that beta-alanine can suppress the growth defect of FEN2 wild-type and fen2 mutant cells on pantothenate-free medium. Evidence is presented that beta-alanine is transported by the general amino acid permease Gap1p. The relation among pantothenate transport, nitrogen catabolite repression, and sensitivity to the antifungal agent fenpropimorph is discussed.

Bakers' yeast is auxotrophic for biotin (vitamin H) and depends on the efficient uptake of this compound from the environment. A mutant strain with strongly reduced biotin uptake and with reduced levels of protein biotinylation was identified. The strain was auxotrophic for long-chain fatty acids, and this auxotrophy could be suppressed with high levels of biotin in the medium. After transformation of this mutant with a yeast genomic library, the unassigned open reading frame YGR065C was identified to complement this mutation. This gene codes for a protein with 593 amino acids and 12 putative transmembrane helices. Northern blot analysis revealed that, in wild-type cells, the corresponding mRNA levels were increased at low biotin concentrations. Likewise, cellular biotin uptake was increased with decreasing biotin availability. Expression of YGR065C under the control of the constitutive ADH1 promoter resulted in very high biotin transport rates across the plasma membrane that were no longer regulated by the biotin concentration in the growth medium. We conclude that YGR065C encodes the first biotin transporter identified for a non-mammalian organism and designate this gene VHT1 for vitamin H transporter 1.

Abstract.: To elucidate the kinetic properties of the Arabidopsis H+/sucrose cotransporter, SUC1, with respect to transmembrane voltage and ligand concentrations, the transport system was heterologously expressed in Xenopus laevis oocytes. Steady-state plasma membrane currents associated with transport of sucrose were measured with two-electrode voltage clamp over the voltage range −180 to +40 mV as a function of extracellular pH and sugar concentrations. At any given voltage, currents exhibited hyperbolic kinetics with respect to extracellular H+ and sugar concentrations, and this enabled determination of values for the maximum currents in the presence of each ligand (i H max , i S max for H+ and sucrose) and of the ligand concentrations eliciting half-maximal currents (K H m , K S m ). The i H max and i S max exhibited marked and statistically significant increases as a function of increasingly negative membrane potential. However, the K H m and K S m decreased with increasingly negative membrane potential. Furthermore, at any given voltage, i S max increased and K S m decreased as a function of the external H+ concentration. Eight six-state carrier models—which comprised the four possible permutations of intracellular and extracellular ligand binding order, each with charge translocation on the sugar-loaded or -unloaded forms of the carrier—were analyzed algebraically with respect to their competence to account for the ensemble of kinetic observations. Of these, two models (first-on, first-off and last-on, first-off with respect to sucrose binding as it passes from outside to inside the cell and with charge translocation on the loaded form of the carrier) exhibit sufficient kinetic flexibility to describe the observations. Combining these two, a single model emerges in which the binding on the external side can be random, but it can only be ordered on the inside, with the sugar dissociating before the proton.

A single genomic clone (14 kb) isolated from bean (Phaseolus vulgaris L.) contains two genes that encode glycine‐rich proteins. These genes are present as single copies in the genome, are separated by 2.85 kb and encode transcripts of 1.8 kb and 1.0 kb respectively. The encoded proteins contain 60% glycine and have amino‐terminal signal peptides. The 1.8 kb transcript is present in young hypocotyls and in ovary tissue. Excision‐wounding transiently induced this transcript in old, but not in young hypocotyl tissue. Antibodies raised against regions of the glycine‐rich protein 1.8, expressed as a lacZ fusion protein in bacteria, react with a protein of 53 kd in a protein fraction extracted from cell walls of bean ovaries. Tissue imprints of bean ovaries treated with anti‐glycine‐rich protein antibodies showed that the glycine‐rich protein was distributed in a regular pattern of small, highly localized discrete sites. The immunoreactive regions correspond to the pattern of vascular tissue in the pod. In young hypocotyls, glycine‐rich protein is present at four pairs of discrete sites symmetrically arranged on the inner side of the vascular ring. These results suggest a close relationship between glycine‐rich proteins and development of the vascular system.

For graphsA andB the relationA?(B)r1 means that for everyr-coloring of the vertices ofA there is a monochromatic copy ofB inA. Forb (G) is the family of graphs which do not embedG. A familyFof graphs is Ramsey if for all graphsB?Fthere is a graphA?Fsuch thatA?(B)r1. The only graphsG for which it is not known whether Forb (G) is Ramsey are graphs which have a cutpoint adjacent to every other vertex except one. In this paper we prove for a large subclass of those graphsG, that Forb (G) does not have the Ramsey property.

We denote byKkl,k, l=2, the set of allk-uniform hypergraphsK which have the property that every l element subset of the base ofK is a subset of one of the hyperedges ofK. So, the only element inK22 are the complete graphs. If I is a subset ofKkl then there is exactly one homogeneous hypergraphHI whose age is the set of all finite hypergraphs which do not embed any element of I. We callHI-free homogeneous graphsHn have been shown to be indivisible, that is, for any partition ofHn into two classes, oue of the classes embeds an isomorphic copy ofHn. [5]. Here we will investigate this question of indivisibility in the more general context ofI-free homogeneous hypergraphs. We will derive a general necessary condition for a homogeneous structure to be indivisible and prove that allI-free hypergraphs for I ?Kkl with l=3 are indivisible. TheI-free hypergraphs with I ?Kk2 satisfy a weaker form of indivisibility which was first shown by Henson [2] to hold forHn. The general necessary condition for homogeneous structures to be indivisible will then be used to show that not allI-free homogeneous hypergraphs are indivisible.

This paper addresses the marking optimization of stochastic timed event graphs, where the transition firing times are generated by random variables with general distributions. The marking optimization problem consists of obtaining a given cycle time while minimizing a p-invariant criterion. We propose two heuristic algorithms, both starting from the optimal solution to the associated deterministic problem and iteratively adding tokens to adequate places as long as the given cycle time is not obtained. Infinitesimal perturbation analysis of the average cycle time with respect to the transition firing times is used to identify the appropriate places in which new tokens are added at each iteration. Numerical results show that the heuristic algorithms provide solutions better than the ones obtained by the existing methods.

One of the problems in the theory of order polynomially complete lattices is the question whether an order polynomially complete lattice is necessarily finite. In this note we give a partial answer to this problem by showing: No unbounded lattice is order polynomially complete. From this we deduce that a polynomially complete lattice cannot be countably infinite.

Autotrophically grown cells of Chlorella vulgaris show a strong increase in the uptake rates for hexoses and for seven amino acids when incubated in the presence of hexoses. This increase is due to de-novo synthesis of three transport proteins: one forhexoses and two for amino acids. Mutants deficient in hexose transport were obtained after treatment of wild-type cells with acridine orange, followed by a selection procedure using the toxic hexose analogue, 2-deoxy-D-glucose. Moreover, the two amino-acid-transport systems could not be induced in these mutants by hexoses. The capacity to phosphorylate hexoses was identical in mutants and in the wild-type strain. The loss of transport activities can be correlated with the loss of certain radiolabeled protein bands on fluorograms of sodium dodecylsulfate-polyacrylamide gels. These proteins are assumed to be responsible for the different transport systems in the wild-type strain. With the help of additional mutants defective in one or two of the different aminoacid-transport systems, it has been attempted to assign the different transport activities to individual protein bands on the gel.

Abstract: The algebraic operations on a set A which admit (as a homomorphism) a particular mapf∈A A, admit all powers off and certain other maps as well. The algebraic closure off, $$\bar f$$ , is the totality of all maps which admit the algebraic operations thatf does. The purpose of this paper is to characterize $$\bar f$$ in terms off, both forA finite and forA infinite.

A monoidM and a latticeL arealgebraic if there is an algebraA with endomorphism monoid EndA ? M and subalgebra lattice SuA ?L. For each chainC we characterize those monoidsM for whichM and C are algebraic. In particular we show that a finite monoidM is algebraic with the three-chain iff the “equalizers” ofM form a chainE =3. The same assertion however fails for infinite monoids. This generalizes the corresponding result for two-chains and solves a problem posed by B. Jónsson ([2], p. 147). We settle the same question for all longer chainsK.

In this paper we show that the number of pairwise nonisomorphic two-dimensional posets with n elements is asymptotically equivalent to 1/2n!. This estimate is based on a characterization, in terms of structural decomposition, of two-dimensional posets having a unique representation as the intersection of two linear extensions.

In 1979, Papadimitriou and Yannakakis gave a polynomial time algorithm for the scheduling of jobs requiring unit completion times when the precedence constraints form an interval order. The authors solve here the corresponding problem, for preemptive scheduling (a job can be interrupted to work on more important tasks, and completed at a later time, subject to the usual scheduling constraints.) The m-machine preemptive scheduling problem is shown to have a polynomial algorithm, for both unit time and variable execution times as well, when the precedence constraints are given by an interval order.

In scheduling jobs subject to precedence constraints that form a partial order, it is advantageous to interrupt (preempt) jobs, and return to complete them at a later time in order to minimize total completion time. It is clearly desirable to see that such preemptive scheduling by finitely many machines requires only intervals of work, and not a more general assignment of tasks over measurable sets, for optimal completion. It is a deeper fact that arbitrarily small intervals are required for a fixed number of machines m>-3 for optimal preemptive scheduling. On the other hand, if the number of jobs is fixed, say n, then it is intuitively clear that it suffices to use only comparatively large intervals (but less clear ‘how large’ will suffice!). The authors address these and certain related questions.

Abstract: A semigroup of functionsS υA A isalgebraic providedA can be endowed with some collection of (finitary) operations to produce an algebraU withS = EndU, the endomorphisms ofU. Thealgebraic closure ofS is $$\bar S$$ =End,U s , whereU s is the algebra of all finitary operations which admit eachf σS as a homomorphism. Here we prove, for A finite, thatg σ $$\bar S$$ iffg is the unique solution to a system ζ of functional equations each of the formfx=h orfx=y with, coefficientsf, h σS. For A infinite a similar local condition holds. Applications to related problems are given.

We have characterized three different transcripts induced by fungal elicitor, wounding, or infection which encode apoproteins of cell wall hydroxyproline-rich glycoproteins involved in plant defense against infection. The proteins encoded by two of these transcripts contain a proline-rich domain involving tandem repetition of the 16-amino-acid unit Tyr3-Lys-Ser-Pro4-Ser-Pro-Ser-Pro4. The third transcript encodes a protein with a proline-rich domain involving a variant of this 16-mer canonical repeat: Tyr3-His-Ser-Pro4-Lys-His-Ser-Pro4. Each transcript is encoded by a separate gene present at single or low copy number in the haploid genome. These transcripts exhibit markedly different patterns of accumulation in different stress conditions, indicating the operation of several distinct intercellular stress signal systems in higher plants.

In autotrophically grown Chlorella cells, glucose induces a hexose transport system but, at the same time, the synthesis of two amino acid transport systems is also induced. Thus, the rates of uptake of glycine, L-alanine, L-proline, and L-serine, all of which compete with each other for entry into the cells, increase more than 100-fold when the algae are pretreated with glucose. The rates of L-arginine and L-lysine uptake increase by a factor of 25 to 50. The accumulation of proline and arginine within the cells amounts to 200- and 600-fold, respectively. Glucose does not cause the positive effect on amino acid uptake by serving as metabolic substrate because the nonmetabolizable 6-deoxyglucose also acts as inducer. Cycloheximide prevents the induction. The induced transport system for the four neutral amino acids has a turnover with a half-life of 7 hr, which corresponds closely to the half-life of the hexose transport system. The transport system for the basic amino acids, on the other hand, disappears with a half-life of 25 hr.

For graphs $ A$ the relation $ A \to (B)_r^1$-coloring of the vertices of $ A$ in $ A$ $ \operatorname{Forb} ({G_1},{G_2}, \ldots ,{G_n})$ $ {G_1},{G_2}, \ldots ,{G_n}$ $ \mathcal{F}$ $ B \in \mathcal{F}$ $ A \in \mathcal{F}$ $ A \to (B)_r^1$ and $ K$ and $ K$ $ \operatorname{Forb} (G,K)$ $ \overline G $ is disconnected then $ \operatorname{Forb} (G,K)$. A family $ \mathcal{F}$age if there is a countable graph $ G$ $ \mathcal{F}$ for which is not an age but has the Ramsey property.

A functionf from the posetP to the posetQ is a strict morphism if for allx, y ? P withx1,q1)<(p2,q2) if and only ifp12 andq12.) This paper proves that well-founded trees with height =? are multiplicative posets.