Identification of angiogenic activity and the cloning and expression of platelet-derived endothelial cell growth factor

Cloning and sequencing of the complementary DNA for platelet-derived endothelial cell growth factor indicates that it is a novel factor distinct from previously characterized proteins. The factor, a protein with a relative molecular mass of about 45,000, stimulates endothelial cell growth and chemotaxis in vitro and angiogenesis in vivo.     

Activation of cell growth by binding of Friend spleen focus-forming virus gp55 glycoprotein to the erythropoietin receptor

Friend spleen focus-forming virus (SFFV) is a defective murine C-type retrovirus which causes a multi-stage erythroleukaemia in mice and erythroblastosis in bone marrow cultures. The SFFV env gene encodes a membrane glycoprotein, gp55, which is located on the cell surface and in the rough endoplasmic reticulum and is essential both for the induction of leukaemia in vivo and erythroblast proliferation in vitro. The mechanism by which gp55 causes increased erythroblastosis and ultimately leukaemia is unknown, but a reasonable suggestion is that gp55 can mimic the action of erythropoietin by binding to its receptor (Epo-R), thereby triggering prolonged proliferation of erythroid cells. To test this possibility, we have co-expressed gp55 and the murine Epo-R in a fibroblast cell line. We show here that in such cells, the SFFV glycoprotein binds directly to Epo-R. Furthermore, when an interleukin-3 (IL-3)-dependent lymphoid cell line was co-infected by SFFV and a virus that carries the Epo-R gene, it could grow without IL-3. We suggest that through direct binding to Epo-R, gp55 can stimulate the receptor and by-pass the normal requirement for Epo, causing prolonged proliferation of infected erythroid cells. This could be the first step of leukaemogenesis induced by Friend virus.     

Production of 'hybrid' antibiotics by genetic engineering

The recent development of molecular cloning systems in Streptomyces has made possible the isolation of biosynthetic genes for some of the many antibiotics produced by members of this important genus of bacteria. Such clones can now be used to test the idea that novel antibiotics could arise through the transfer of biosynthetic genes between streptomycetes producing different antibiotics. The likelihood of a 'hybrid' compound being produced must depend on the substrate specificities of the biosynthetic enzymes, about which little is known. In attempts to demonstrate hybrid antibiotic production, we therefore began with strains producing different members of the same chemical class of compounds in order to maximize the chance of success. Here we report the production of novel compounds by gene transfer between strains producing the isochromanequinone antibiotics actinorhodin, granaticin and medermycin. These experiments were made possible by the recent cloning of the whole set of genes for the biosynthetic pathway of actinorhodin from Streptomyces coelicolor A3(2) (ref. 8). We believe that this represents the first report of the production of hybrid antibiotics by genetic engineering.     

Intergeneric interactions between Eimeria separata (Apicomplexa) and Nippostrongylus brasiliensis (Nematoda) in the rat

Ova production in Nippostrongylus brasiliensis infected rats was significantly greater than in rats singly infected with the helminth when Eimeria separata infections were introduced 4, 6 and 11 days postinoculation with N. brasiliensis. Patent periods were unaltered during concurrent infections. These results suggest that the presence of E. separata affects helminth fecundity but does not increase N. brasiliensis longevity as has been shown with E. nieschulzi.     

Independence of the circadian rhythm in alertness from the sleep/wake cycle

It is common knowledge that our feelings of alertness or drowsiness vary throughout the day. Indeed, this diurnal variation is so widely accepted that it has been used to validate the drowsy/alert component of activation obtained from mood adjective checklists. There is, however, some evidence from sleep deprivation and shiftwork studies that this variation is not simply a reflection of our sleep/wake cycle, as might be expected, but is at least partially dependent on an endogenous circadian (approximately 24 h) oscillator such as that proposed to account for the circadian rhythm in body temperature and other physiological variables. Here we have tested this suggestion by separating the body-temperature rhythm from the sleep/wake cycle by progressively shortening artificial time cues (zeitgebers). Our results indicate that the circadian rhythm in alertness can become independent of both the sleep/wake cycle and the rhythm in body temperature. Further, and contrary to our expectations, the results suggest that the sleep/wake cycle exerts less influence on the alertness rhythm than it does on that of temperature.     

Local protein-DNA interactions may determine nucleosome positions on yeast plasmids

The structure of the nucleosome core particle, the basic structural subunit of chromatin, is well known. Although nucleosomes often appear to be positioned randomly with respect to DNA sequences, in some cases they seem to occupy precisely defined positions on the DNA. The yeast plasmid TRP1ARS1 contains three precisely positioned, stable nucleosomes, I, II and III, which are flanked by nuclease-sensitive regions. Our aim in the present study was to determine whether the positions of these three nucleosomes relate to (1) protein-DNA interactions; (2) the limited space between nuclease-sensitive regions, which is just long enough to accommodate three yeast nucleosomes (that is, boundary conditions); or (3) proximity to the putative origin of replication in one of the nuclease-sensitive regions. We have tested these alternatives by analysing the positions of nucleosomes after insertion of various lengths of DNA into this region and assembly of chromatin in vivo. Our results suggest that specific protein-DNA interactions are the most likely determinants of these nucleosome positions.