Interferon inhibits DNA Synthesis induced in Mouse Lymphocyte Suspensions by Phytohaemagglutinin or by Allogeneic Cells

IN addition to its well known antiviral activity, interferon has recently been shown to inhibit the multiplication of tumour and mammalian cells in cell culture^1–6. We report here the inhibition by interferon of DNA synthesis induced in mouse spleen lymphocytes by the non-viral stimuli phytohaemagglutinin (PHA) and allogeneic lymphocytes. These findings are in accord with our contention that interferon affects cell function and, furthermore, they suggest that by acting on lymphocytes, interferon plays a role in the immunological response of the host.     

Two Amino-acid Carriers in Pea Chloroplasts

CHLOROPLASTS are more permeable to amino-acids^1,2 than are cell membranes³ and also discriminate between their optical isomers². This has led to the suggestion that the passage of amino-acids through the limiting membranes of chloroplasts is facilitated by carriers². Using the additional criteria of saturation and competition, we support this suggestion and show that at least two carriers are probably involved.     

An antigenic HIV-1 peptide sequence engineered into the surface structure of transferrin does not elicit an antibody response.

One novel approach for the biological delivery of peptide drugs is to incorporate the sequence of the peptide into the structure of a natural transport protein such as human serum transferrin (HST). However, a potential drawback is that the HST may increase the immunoreactivity of the peptide, in the same way that carrier proteins can be used to generate highly immunogenic peptide hapten conjugates. In this study we have generated a recombinant HST carrier protein that contains a peptide substrate of HIV-1 protease (VSQNYPIVL). The protein retained native HST function, and the peptide was surface exposed since it was immunoreactive in native dot blots, and was cleaved by HIV-1 protease. Immunisation of rabbits with the recombinant protein elicited only a very poor anti-peptide immune response. In contrast, strong anti-peptide immune responses were raised against both the peptide alone, and a chemical conjugate of the peptide with HST. These data demonstrate that it is possible to attenuate the immune response normally directed against an immunogenic peptide sequence by engineering into a surface exposed loop of HST. These findings may have an important impact on the future design of peptide delivery systems.     

<Superscript>15</Superscript>N natural abundance of fossil peat reflects the influence of animal-derived nitrogen on vegetation

'¹⁵N signatures of fossil peat were used to interpret past ecosystem processes on tectonically active subantarctic Macquarie Island. By comparing past vegetation reconstructed from the fossil record with present-day vegetation analogues, our evidence strongly suggests that changes in the '¹⁵N signatures of fossil peat at this location reflect mainly past changes in the proportion of plant nitrogen derived from animal sources. Associated with uplift above sea level over the past 8,500 years, fossil records in two peat deposits on the island chronicle a change from coastal vegetation with fur and elephant seal disturbance to the existing inland herbfield. Coupled with this change are synchronous changes in the '¹⁵N signatures of peat layers. At two sites ¹⁵N-enriched peat '¹⁵N signatures of up to +17‰ were associated with a high abundance of pollen of the nitrophile Callitriche antarctica (Callitrichaceae). At one site fossil seal hair was also associated with enriched peat '¹⁵N. Less ¹⁵N enriched '¹⁵N signatures (e.g. -1.9‰ to +3.9‰) were measured in peat layers which lacked animal associated C. antarctica and Acaena spp. Interpretation of a third peat profile indicates continual occupation of a ridge site by burrowing petrels for most of the Holocene. We suggest that ¹⁵N signatures of fossil peat remained relatively stable with time once deposited, providing a significant new tool for interpreting the palaeoecology.     

Interaction of RNA with transformed glucocorticoid receptor. I. Isolation and purification of the RNA

The glucocorticoid receptor (GR) from mouse AtT-20 pituitary tumor cells, when transformed using a variety of in vitro protocols, yields a DNA-binding RNA-containing 6 S form. In order to better understand the physiological role of RNA interaction with the transformed GR, we have isolated and purified the putative RNA from AtT-20 cells. [3H]Triamcinolone acetonide-labeled cytosolic GR was transformed, using Sephadex G-25 filtration, to yield the RNA-containing 6 S GR. The transformed 6 S GR was separated on DEAE-cellulose into the 4 S GR (eluting at about 100 mM KCl) while its associated RNA eluted at 0.30-0.45 M KCl. The addition of only these RNA fractions to the 4 S GR can reconstitute 6 S GR as shown on 5-20% sucrose gradients. RNA (0.3-0.45 M KCl fractions) was further purified by hydroxylapatite chromatography, and the bound RNA (eluted at approximately 70 mM PO4(-2)) was then loaded onto preparative 5-20% sucrose gradients to separate RNA on the basis of size (sedimentation rate). A uniform class of RNA sedimenting at 4 S was obtained and then adsorbed to oligo(dT)-cellulose columns. The unbound fraction (poly(A-)) was capable of shifting 4 S GR to 6 S. Using these chromatographic procedures about 90% of the cellular RNA, incapable of reconstituting the 6 S GR from the 4 S form, was eliminated. The 4 S GR was covalently cross-linked with the purified RNA (termed PIVB RNA) using formaldehyde. The resulting cross-linked GR X RNA complexes were shown to sediment at the density of ribonucleoprotein (1.38 g/cm3) in CsCl gradients and at the 6 S position in high salt sucrose gradients. The hydrolysis of PIVB RNA with ribonuclease A prevented the formation of high salt-resistant ribonucleoprotein complexes, indicating that the GR may be in close contact with PIVB RNA. Electrophoresis of the PIVB RNA on 5% agarose-formaldehyde-denaturing gels yielded one major band with a molecular size of approximately 75 bases. It thus appears that an endogenous 4 S RNA (PIVB RNA) of about 25 kDa specifically interacts with the monomeric 4 S GR to yield the 6 S GR.