Mitochondrial transmission during mating in Saccharomyces cerevisiae is determined by mitochondrial fusion and fission and the intramitochondrial segregation of mitochondrial DNA

To gain insight into the process of mitochondrial transmission in yeast, we directly labeled mitochondrial proteins and mitochondrial DNA (mtDNA) and observed their fate after the fusion of two cells. To this end, mitochondrial proteins in haploid cells of opposite mating type were labeled with different fluorescent dyes and observed by fluorescence microscopy after mating of the cells. Parental mitochondrial protein markers rapidly redistributed and colocalized throughout zygotes, indicating that during mating, parental mitochondria fuse and their protein contents intermix, consistent with results previously obtained with a single parentally derived protein marker. Analysis of the three-dimensional structure and dynamics of mitochondria in living cells with wide-field fluorescence microscopy indicated that mitochondria form a single dynamic network, whose continuity is maintained by a balanced frequency of fission and fusion events. Thus, the complete mixing of mitochondrial proteins can be explained by the formation of one continuous mitochondrial compartment after mating. In marked contrast to the mixing of parental mitochondrial proteins after fusion, mtDNA (labeled with the thymidine analogue 5-bromodeoxyuridine) remained distinctly localized to one half of the zygotic cell. This observation provides a direct explanation for the genetically observed nonrandom patterns of mtDNA transmission. We propose that anchoring of mtDNA within the organelle is linked to an active segregation mechanism that ensures accurate inheritance of mtDNA along with the organelle.     

Use of lectins to characterize plasma membrane preparations from boar spermatozoa: a novel technique for monitoring membrane purity and quantity

The object of this study was to develop a method to quantify the amount of outer acrosomal membrane material in isolated plasma membranes from boar sperm cells. The cells were fractionated by nitrogen cavitation, and plasma membranes were isolated by subsequent differential centrifugation steps. Marker enzyme measurement showed that the plasma membrane isolates were enriched in plasma membrane markers and did not contain nuclei, inner acrosomal membranes, or mitochondria. Since there is no marker enzyme known for the outer acrosomal membrane, lectins were used for the detection of this membrane. The membrane specificity of a number of lectin conjugates was tested with fluorescence microscopy and transmission electron microscopy. Membrane binding of these lectin conjugates was quantified with flow-cytometry and an enzyme-linked lectin binding assay. Wheat germ agglutinin was specific for the plasma membrane while peanut agglutinin was specific for the outer acrosomal membrane. The use of these lectins made it possible for the first time to discriminate between these two membranes. The isolated plasma membrane fraction was enriched more than 10-fold (17-fold after further purification by a sucrose gradient) in plasma membrane material compared to outer acrosomal membrane material. Highly purified sperm plasma membranes should prove to be useful for research on primary sperm-zona interactions.     

Mandibular reconstruction with transforming growth factor-beta1

This is a case report of a 43-year-old woman who received a transplant for end-stage liver disease due to hereditary hemorrhagic telangiectasia and fibropolycystic liver disease. This is an uncommon association of two autosomal-dominant conditions with defined genetic and molecular defects. The liver showed extensive vascular malformations of arteries and veins as well as telangiectasia and fibrosis. In addition, there were cystically dilated ducts containing inspissated bile and extensive von Meyenburg complexes. This case raises interesting questions about the possible relationship of these genes and their gene products, both of which are related to cell-matrix interactions and are strongly associated with blood vessels, one of them being expressed on endothelial cells and the other being developmentally important in blood vessels.     

Antiretroviral therapies

We describe an algorithm which enables us to search the conformational space of the side chains of a protein to identify the global minimum energy combination of side chain conformations as well as all other conformations within a specified energy cutoff of the global energy minimum. The program is used to explore the side chain conformational energy surface of a number of proteins, to investigate how this surface varies with the energy model used to describe the interactions within the system and the rotamer library. Enumeration of the rotamer combinations enables us to directly evaluate the partition function, and thus calculate the side chain contribution to the conformational entropy of the folded protein. An investigation of these conformations and the relationships between them shows that most of the conformations near to the global energy minimum arise from changes in side chain conformations that are essentially independent; very few result from a concerted change in conformation of two or more residues. Some of the limitations of the approach are discussed.     

Structural analysis of substrate binding by the molecular chaperone DnaK

DnaK and other members of the 70-kilodalton heat-shock protein (hsp70) family promote protein folding, interaction, and translocation, both constitutively and in response to stress, by binding to unfolded polypeptide segments. These proteins have two functional units: a substrate-binding portion binds the polypeptide, and an adenosine triphosphatase portion facilitates substrate exchange. The crystal structure of a peptide complex with the substrate-binding unit of DnaK has now been determined at 2.0 angstroms resolution. The structure consists of a beta-sandwich subdomain followed by alpha-helical segments. The peptide is bound to DnaK in an extended conformation through a channel defined by loops from the beta sandwich. An alpha-helical domain stabilizes the complex, but does not contact the peptide directly. This domain is rotated in the molecules of a second crystal lattice, which suggests a model of conformation-dependent substrate binding that features a latch mechanism for maintaining long lifetime complexes.     

Cost of management of patients with haemophilia

The cost of managing 114 adult haemophiliacs in the west of Scotland was assessed for the period 1 March 1971 to 28 February 1974. Altogether 23 of them (20%) accounted for 80% of the resources used. The cost of hospital treatment of these patients during the period was compared with the predicted cost of home treatment, given the availability of freeze-dried factor VIII concentrate in sufficient amounts. We calculate that adequate on-demand home treatment would cost only 16% more than the present treatment, which is substantially less efficient.