Although entrepreneurship has become a buzzword in the public debate, a coherent definition of entrepreneurship has not yet emerged. In this paper, we review and compare the most common theoretical definitions of entrepreneurship in economics and discuss their connection to the various empirical measures in use. We argue that entrepreneurship is best considered a multifaceted concept, and that the different empirical measures reflect different aspects of entrepreneurship. The relevance of this exercise is illustrated by the fact that in a cross-country comparison of entrepreneurship, we find that the relative ranking of countries depends crucially on the indicator used.

Background: The filamentous fungus, Aspergillus niger, responds to nutrient availability by modulating secretion of various substrate degrading hydrolases. This ability has made it an important organism in industrial production of secreted glycoproteins. The recent publication of the A. niger genome sequence and availability of microarrays allow high resolution studies of transcriptional regulation of basal cellular processes, like those of glycoprotein synthesis and secretion. It is known that the activities of certain secretory pathway enzymes involved Nglycosylation are elevated in response to carbon source induced secretion of the glycoprotein glucoamylase. We have investigated whether carbon source dependent enhancement of protein secretion can lead to upregulation of secretory pathway elements extending beyond those involved in N-glycosylation.

Ribosomal RNA from all organisms contains post-transcriptionally modified nucleotides whose function is far from clear. To gain insight into the molecular interactions of modified nucleotides, we investigated the modification status of Thermus thermophilus 5 S and 23 S ribosomal RNA by mass spectrometry and chemical derivatization/primer extension. A total of eleven modified nucleotides was found in 23 S rRNA, of which eight were singly methylated nucleotides and three were pseudouridines. These modified nucleotides were mapped into the published three-dimensional ribosome structure. Seven of the modified nucleotides located to domain IV, and four modified nucleotides located to domain V of the 23 S rRNA. All posttranscriptionally modified nucleotides map in the center of the ribosome, and none of them are in contact with ribosomal proteins. All except one of the modified nucleotides were found in secondary structure elements of the 23 S ribosomal RNA that contact either 16 S ribosomal RNA or transfer RNA, with five of these nucleotides physically involved in intermolecular RNA-RNA bridges. These findings strongly suggest that the posttranscriptional modifications play a role in modulating intermolecular RNA-RNA contacts, which is the first suggestion on a specific function of endogenous ribosomal RNA modifications.All cellular protein synthesis is performed by ribosomes, which are large ribonucleoprotein particles. The prokaryote ribosome consists of two stable and separable entities, a 50 S and a 30 S subunit. The 50 S subunit contains two rRNAs of ϳ3000 and 120 nucleotides (23 S and 5 S rRNA, respectively) and around 35 proteins, whereas the 30 S subunit contains 16 S rRNA of ϳ1600 nucleotides and around 20 proteins; the exact numbers vary with the species. Eukaryotic ribosomes are larger, but structural features are remarkably conserved between the domains of life.rRNAs are post-transcriptionally modified at specific nucleotides, but the number of modified nucleotides varies greatly. The large ribosomal RNA in mitochondria contains just a few modified nucleotides (1), Escherichia coli 23 S rRNA has 25 (2, 3), whereas over 100 are found in vertebrate cytoplasmic 28 S rRNA (4). The function of post-transcriptional rRNA modifications is far from clear, although they have been implicated in various processes. Specific rRNA methylation is used by numerous antibiotics-producing microorganisms as a means of autoprotection (see e.g. Refs. 5 and 6), but only a small fraction of post-transcriptional modifications can be assigned to this well defined function. E. coli 23 S rRNA modifications cluster in functionally principal parts of the ribosome such as the peptidyl transferase center and inter-subunit bridges when modeled into the structure of the Haloarcula marismortui large ribosomal subunit (7). The modified nucleotides in the central domains of 23 S rRNA from H. marismortui itself are all located in regions of intra-or intermolecular RNA-RNA contact (8) suggesting structure stabilization.The post-transcriptionall...

Growth of the green algae Chlamydomonas reinhardtii and Chlorella sp. in batch cultures was investigated in a novel gas-tight photobioreactor, in which CO 2 , H 2 , and N 2 were titrated into the gas phase to control medium pH, dissolved oxygen partial pressure, and headspace pressure, respectively. The exit gas from the reactor was circulated through a loop of tubing and re-introduced into the culture. CO 2 uptake was estimated from the addition of CO 2 as acidic titrant and O 2 evolution was estimated from titration by H 2 , which was used to reduce O 2 over a Pd catalyst. The photosynthetic quotient, PQ, was estimated as the ratio between O 2 evolution and CO 2 up-take rates. NH 4 + , NO 2 − , or NO 3 − was the final cell density limiting nutrient. Cultures of both algae were, in general, characterised by a nitrogen sufficient growth phase followed by a nitrogen depleted phase in which starch was the major product. The estimated PQ values were dependent on the level of oxidation of the nitrogen source. The PQ was 1 with NH 4 + as the nitrogen source and 1.3 when NO 3 − was the nitrogen source. In cultures grown on all nitrogen sources, the PQ value approached 1 when the nitrogen source was depleted and starch synthesis became dominant, to further increase towards 1.3 over a period of 3-4 days. This latter increase in PQ, which was indicative of production of reduced compounds like lipids, correlated with a simultaneous increase in the degree of reduction of the biomass. When using the titrations of CO 2 and H 2 into the reactor headspace to estimate the up-take of CO 2 , the production of O 2 , and the PQ, the rate of biomass production could be followed, the stoichiometrical composition of the produced algal biomass could be estimated, and different growth phases could be identified.

This is a study of high-affinity glucose uptake in Aspergillus niger and the effect of disruption of a high-affinity monosaccharide-transporter gene, mstA. The substrate saturation constant (K s ) of a reference strain was about 15 mM in glucose-limited chemostat culture. Disruption of mstA resulted in a two-to fivefold reduction in affinity for glucose and led to expression of a low-affinity glucose transport gene, mstC, at high dilution rate. The effect of mstA disruption was more subtle at low and intermediate dilution rates, pointing to some degree of functional redundancy in the high-affinity uptake system of A. niger. The mstA disruptant and a reference strain were cultivated in glucose-limited chemostat cultures at low, intermediate and high dilution rate (D50.07 h "1 , 0.14 h "1 and 0.20 h "1 ). Mycelium harvested from steady-state cultures was subjected to glucose uptake assays, and analysed for expression of mstA and two other transporter genes, mstC and mstF. The capacity for glucose uptake (v max ) of both strains was significantly reduced at low dilution rate. The glucose uptake assays revealed complex uptake kinetics. This impeded accurate determination of maximum specific uptake rates (v max ) and apparent affinity constants (K app m ) at intermediate and high dilution rate. Two high-affinity glucose transporter genes, mstA and mstF, were expressed at all three dilution rates in chemostat cultures, in contrast to batch culture, where only mstC was expressed. Expression patterns of the three transporter genes suggested differential regulation and functionality of their products.