In Vivo Dynamics of Nuclear Pore Complexes in Yeast

While much is known about the role of nuclear pore complexes (NPCs) in nucleocytoplasmic transport, the mechanism of NPC assembly into pores formed through the double lipid bilayer of the nuclear envelope is not well defined. To investigate the dynamics of NPCs, we developed a live-cell assay in the yeast Saccharomyces cerevisiae. The nucleoporin Nup49p was fused to the green fluorescent protein (GFP) of Aequorea victoria and expressed in nup49 null haploid yeast cells. When the GFP–Nup49p donor cell was mated with a recipient cell harboring only unlabeled Nup49p, the nuclei fused as a consequence of the normal mating process. By monitoring the distribution of the GFP–Nup49p, we could assess whether NPCs were able to move from the donor section of the nuclear envelope to that of the recipient nucleus. We observed that fluorescent NPCs moved and encircled the entire nucleus within 25 min after fusion. When assays were done in mutant kar1-1 strains, where nuclear fusion does not occur, GFP–Nup49p appearance in the recipient nucleus occurred at a very slow rate, presumably due to new NPC biogenesis or to exchange of GFP– Nup49p into existing recipient NPCs. Interestingly, in a number of existing mutant strains, NPCs are clustered together at permissive growth temperatures. This has been explained with two different hypotheses: by movement of NPCs through the double nuclear membranes with subsequent clustering at a central location; or, alternatively, by assembly of all NPCs at a central location (such as the spindle pole body) with NPCs in mutant cells unable to move away from this point. Using the GFP–Nup49p system with a mutant in the NPCassociated factor Gle2p that exhibits formation of NPC clusters only at 37°C, it was possible to distinguish between these two models for NPC dynamics. GFP– Nup49p-labeled NPCs, assembled at 23°C, moved into clusters when the cells were shifted to growth at 37°C. These results indicate that NPCs can move through the double nuclear membranes and, moreover, can do so to form NPC clusters in mutant strains. Such clusters may result by releasing NPCs from a nuclear tether, or by disappearance of a protein that normally prevents pore aggregation. This system represents a novel approach for identifying regulators of NPC assembly and movement in the future.     

Genetic dissection of herbicide tolerance in maize by molecular markers

In order to detect the genetic architecture of maize tolerance to Alachlor, a widely used chloroacetanilide, linkage analysis between the expression of the trait and allelic composition of molecular markers was performed. The experiment was carried out on a population of 142 recombinant inbred lines, developed starting from the F₁ between two lines with different reactivity to the herbicide, and self-fertilized for 10 generations; the lines were typed by 48 RFLP markers and 66 microsatellites (SSR). Besides seedling tolerance, evaluated as proportion of normal (non-injured) plants after herbicide treatment, other minor components of tolerance were studied: seed germination ability, pollen germination and tube growth in the presence of the herbicide. The analysis, performed by three statistical methods, revealed the presence of factors controlling seedling tolerance on seven chromosomal regions. Five QTLs appeared to be involved in seed germination ability in the presence of Alachlor, four QTLs in pollen tolerance in terms of germination and four in tube growth under stress were detected. Three loci, on chromosomes 1, 7 and 10, explained most of the variation of seedling tolerance, thus being interesting candidate for marker-assisted selection.     

The essential dynamics of Cu, Zn superoxide dismutase: suggestion of intersubunit communication.

A 300-ps molecular dynamics simulation of the whole Cu, Zn superoxide dismutase dimer has been carried out in water, and the trajectory has been analyzed by the essential dynamics method. The results indicate that the motion is defined by few preferred directions identified by the first four to six eigenvectors and that the motion of the two monomers at each instant is not symmetrical. The vectors symmetrical to the eigenvectors are significantly sampled, suggesting that, on average, the motions of the two subunits will exchange. Large intra- and intersubunit motions involving different subdomains of the protein are observed. A mechanical coupling between the two subunits is also suggested, because displacements of the loops surrounding the active site in one monomer are correlated with the motion of parts of the second toward the intersubunit interface.     

The yeast DNA polymerase-primase complex: genes and proteins

The yeast DNA polymerase-primase complex is composed of four polypeptides designated p180, p74, p58 and p48. All the genes coding for these polypeptides have now been cloned. By protein sequence comparison we found that yeast DNA polymerase I (alpha) shares three major regions of homology with several DNA polymerases. A fourth region, called region P, is conserved in yeast and human DNA polymerase alpha. The site of a temperature-sensitive mutation in the POL1 gene which causes decreased stability of the polymerase-primase complex has been sequenced and falls in this region. We hypothesize that region P is important for protein-protein interactions. Highly selective biochemical methods might be similarly important to distinguish functional domains in the polymerase-primase complex. An autocatalytic affinity labeling procedure has been applied to map the active center of yeast DNA primase. From this approach we conclude that both primase subunits (p48 and p58) participate in the formation of the catalytic site of the enzyme.     

A 9-bp deletion (2320del9) on the background of the arylsulfatase A pseudodeficiency allele in a metachromatic leukodystrophy patient and in a patient with nonprogressive neurological symptoms

A 9-bp deletion (2320del9) was detected in the arylsulfatase A genes of a patient with late infantile metachromatic leukodystrophy and of a patient with nonprogressive neurological symptoms and very low arylsulfatase A activity. Both patients are heterozygous for the deletion, which involves codons 406–408 and causes loss of a Ser-Asp-Thr tract in the predicted protein. In both patients the 9-bp deletion lies in a pseudodeficiency allele. The patient with metachromatic leukodystrophy carries the common 459 + 1G > A mutation in the other allele. The other patient is homozygous for the pseudodeficiency allele, and consequently is a compound heterozygote for a metachromatic leukodystrophy allele and a pseudodeficiency allele. We hypothesize that the compound heterozygosity predisposes to the development of nonprogressive neurological symptoms in the presence of additional, still unknown, genetic or nongenetic factors. Received: 18 April 1997 / Accepted: 16 August 1997     

Ragweed pollen: The aeroallergen is spreading in Italy

Presently in Europe, ragweed pollen as an aeroallergen is not as important as Poaceae,Parietaria or Betulaceae, even if in some countries the plant is beginning to influence the local composition of the airborne pollen spectra. In northern Italy, the presence of ragweed airborne pollen has only been reported since the beginning of the 1980’s and it is increasingly spreading from year to year. Given this situation, the allergologists have begun to regard the potential risk of sensitisation to ragweed pollen with much attention. Up to now, such pollen has not been included in the routine allergological tests. In 1995 in some sites of northern Italy (Turin, Milan, Trieste), the concentration values of ragweed pollen were remarkable (∼ 20–30 p/m³) and on the increase with respect to the previous years. This investigation aims at focusing the atmospheric concentration trend on this new aeroallergen (Ambrosia sp.) in Italy from 1991 throughout 1995.     

Do unpublished data help to redraw distributions? The case of the spectacled bear in Peru

Mammal Research - Data availability remains a principal factor limiting the use of species distribution models (SDMs) as tools for wildlife conservation and management of rare species. Although...     

Evolutionary conservativeness of electric field in the Cu,Zn superoxide dismutase active site. Evidence for co-ordinated mutation of charged amino acid residues.

Equipotential lines were calculated, using the Poisson-Boltzmann equation, for six Cu,Zn superoxide dismutases with different protein electric charge and various degrees of sequence homology, namely those from ox, pig, sheep, yeast, and the isoenzymes A and B from the amphibian Xenopus laevis. The three-dimensional structures of the porcine and ovine superoxide dismutases were obtained by molecular modelling reconstruction using the structure of the highly homologous bovine enzyme as a template. The three-dimensional structure of the evolutionary distant yeast Cu,Zn superoxide dismutase was recently resolved by us, while computer-modelled structures are available for X. laevis isoenzymes. The six proteins display large differences in the net protein charge and distribution of electrically charged surface residues but the trend of the equipotential lines in the proximity of the active sites was found to be constant in all cases. These results are in line with the very similar catlytic rate constants experimentally measured for the corresponding enzyme activities. This analysis shows that electrostatic guidance for the enzyme-substrate interaction in Cu,Zn superoxide dismutases is related to a spatial distribution of charges, arranged so as to maintain, in the area surrounding the active sites, an identical electrostatic potential distribution, which is conserved in the evolution of this protein family.