Dual Binding Mode of the Nascent Polypeptide-associated Complex Reveals a Novel Universal Adapter Site on the Ribosome

Nascent polypeptide-associated complex (NAC) was identified in eukaryotes as the first cytosolic factor that contacts the nascent polypeptide chain emerging from the ribosome. NAC is present as a homodimer in archaea and as a highly conserved heterodimer in eukaryotes. Mutations in NAC cause severe embryonically lethal phenotypes in mice, Drosophila melanogaster, and Caenorhabditis elegans. In the yeast Saccharomyces cerevisiae NAC is quantitatively associated with ribosomes. Here we show that NAC contacts several ribosomal proteins. The N terminus of βNAC, however, specifically contacts near the tunnel exit ribosomal protein Rpl31, which is unique to eukaryotes and archaea. Moreover, the first 23 amino acids of βNAC are sufficient to direct an otherwise non-associated protein to the ribosome. In contrast, αNAC (Egd2p) contacts Rpl17, the direct neighbor of Rpl31 at the ribosomal tunnel exit site. Rpl31 was also recently identified as a contact site for the SRP receptor and the ribosome-associated complex. Furthermore, in Escherichia coli peptide deformylase (PDF) interacts with the corresponding surface area on the eubacterial ribosome. In addition to the previously identified universal adapter site represented by Rpl25/Rpl35, we therefore refer to Rpl31/Rpl17 as a novel universal docking site for ribosome-associated factors on the eukaryotic ribosome.     

Leydig cell mitoses in human testes bearing early germ cell tumors

Summary Numerous mitoses were noted in testicular tissue from adult men with early germ cell tumors. More than 15 Leydig cells undergoing mitosis were found in the interstitial compartment. The presence of specific crystalline intracytoplasmatic inclusions demonstrated for the first time that differentiated Leydig cells are capable of proliferation. Occasionally cells are difficult to discriminate during mitosis. To establish reference criteria, the light- and electron-microscopic features of the following mitotic cells were examined: Leydig cells, fibroblasts, perivascular cells, peritubular cells, and lymphocytes. Supplementary mitoses in germ cell tumors and in a case of Leydig cell tumor were investigated. In the literature, only single reports of mitoses in Leydig cells are available. The frequent incidence of Leydig cell mitosis in early germ cell tumors may be due to the presence of growth-promoting factors in the testicular tissue.     

No evidence for linkage of autosomal dominant proximal spinal muscular atrophies to chromosome 5q markers

Summary Two recent articles have reported the linkage of a gene for recessive spinal muscular atrophy (SMA) on the chromosome region 5q11.2–13.3. Our data show no linkage of the dominantly inherited forms of SMA to this chromosome region.     

Synthesis patterns of a set of follicle cell proteins in Drosophila melanogaster sibling species

The protein synthesis pattern of a set of stage and tissue specific proteins has previously been described in Drosophila melanogaster. The analysis of this set of follicle cell proteins (Fc proteins) is here extended to cover several sibling species of Drosophila melanogaster, namely D. simulans, D. mauritiana, D. erecta and D. yakuba. Even though a similar set of proteins were synthesized in these species, minor differences in size of the proteins were found between the species. Some of the species exhibited variation within species.     

Carp myogens of white and red muscles. Properties and amino acid composition of the main low-molecular-weight components of white muscle

1. The three main components of the 1·5–2s ultracentrifugal peak of carp myogen (white muscle) have been isolated by ammonium sulphate fractionation and zone electrophoresis, and crystallized. 2. The molecular weights of these three proteins were determined by sedimentation and diffusion, by the Archibald method and by amino acid analysis, and found to lie between 9000 and 13000. 3. Their complete amino acid compositions were determined by column chromatography and by their ultraviolet spectra. Both methods revealed abnormal compositions, including the absence of tryptophan and methionine and the presence of large amounts of phenylalanine. At most 1 residue each of tyrosine, cysteine, proline, arginine and histidine was found/molecule. 4. The specific viscosity of component 3 was lower than that of other small globular proteins described so far, a fact that suggests that these proteins approximate more closely to the ideal case of the spherical protein molecule. Also, the presence of a single residue of several amino acids, the absence of disulphide bonds, and the apparent reversibility of denaturation by urea of component 3 suggest that the study of these molecules could provide new information on the structure of proteins.     

Optimization of culture conditions for human corneal endothelial cells

Summary Long-term cultivation of human corneal endothelial cells (HCEC) was optimized with respect to different components of the culture system: 25 different nutrient media, different sera, 6 mitogens and various substrates were tested in their ability to influence clonal growth and morphology of HCEC. F99, a 1∶1 mixture of the two media M199 and Ham’s F12, was the most effective basal medium in promoting clonal growth of HCEC. Among various sera, human serum and fetal bovine serum showed optimal growth promoting activities in combination with F99, whereas newborn bovine serum (NBS) was by far superior for the development of a typically corneal endothelial morphology. Crude fibroblast growth factor (FGF), or alternatively endothelial cell growth supplement, was absolutely essential for clonal growth of HCEC at low serum concentrations, for example 5% NBS. Formation of a monolayer with a morphology similar to corneal endothelium in vivo was observed only on culture dishes coated with basal membrane components such as collagen type IV, laminin, or fibronectin. The most pronounced effect on morphologic appearance was obtained by culturing the cells on the extracellular matrix (ECM) produced by bovine corneal endothelial cells. Moreover, ECM could substitute for crude FGF in clonal growth assays.