Production of enterotoxin A by supposedly nonenterotoxigenic Staphylococcus aureus strains.

The production of staphylococcal enterotoxins A (SEA) and B (SEB) was studied by inoculating six well-defined staphylococcal collection strains into cow's, goat's, or sheep's milk (individually or as a 50% mixture of cow's + goat's or cow's + sheep's), into brain heart infusion, and into a medium generally used to enhance the synthesis of enterotoxins (3+3 medium). Four of the strains used are considered to be SEB producers, another is considered an SEA producer, and the remaining strain is nonenterotoxigenic but produces large quantities of staphylococcal protein A. Staphylococcal protein A masked the results in most cases. Only one strain secreted exclusively SEB, while the other three SEB producers synthesized SEA in different amounts. We conclude that enterotoxin production depends on the natural substrate and may differ from the results obtained when the strain is grown on cellophane over agar to determine its toxigenicity.     

In vitro transport of ornithine carbamoyltransferase precursor into rat liver mitochondria using a more homologous medium

The precursor of ornithine carbamoyltransferase can be transported in vitro into rat liver mitochondria using the postmitochondrial supernatant from rat liver, a more homologous medium than the commonly used rabbit reticulocyte lysate. The transport of the precursor in the case of reticulocyte lysate requires a standard translation mixture. In the presence of the postmitochondrial supernatant the same is true. However, when the components of the translation mixture were added individually to the postmitochondrial supernatant, it was found that spermidine or spermine, at physiological concentrations, sufficed for the transport of the precursor of ornithine carbamoyltransferase. The activity of the postmitochondrial supernatant was inactivated by trypsin and slightly decreased by RNase treatment; it was not lost by dialysis or by heating at 100 degrees C.     

Recognition and use of the unusual X-DNA as a primer-template by Klenow DNA polymerase enzyme

Based on CD spectra, 2-amino-2'-deoxyadenosine-containing synthetic alternating DNA, poly(amino2dA-dt) undergoes a conformational transition from a B-form to a non-Z zig-zag form of DNA, called X, even under conditions where enzymes can work. Kinetic parameters of the E. coli Klenow DNA polymerase enzyme-catalyzed copying of both the B- and X-forms of poly(amino2dA-dT) have been determined. Binding affinity of X-DNA to the enzyme proved to be even higher than that of the B-DNA; primer-chain extension of X-poly(amino2dA-dT) was however hindered as compared to its B-form. This differential utilization of X-DNA versus B-DNA by a DNA polymerase is an in vitro enzymatic evidence of an unusual DNA conformation.     

Phorbol esters inhibit apoptosis in IL-2-dependent T lymphocytes

The effect of phorbol esters on the proliferation and survival of interleukin-2(IL-2)-dependent cells was studied using an IL-2-dependent T cell line (CTLL-2) and blasts of BALB/c mouse spleen cells stimulated with Concanavalin A. Addition of phorbol 12,13-dibutyrate (PDBu) to CTLL-2 or ConA blasts induces a mitogenic response which is 25-40% of that elicited by IL-2. Interleukin 2 deprivation leads to a marked decline in the number of viable cells (50% of CTLL-2 cells have died after 8-10 hours incubation in IL-2-free medium). The mechanism of cell death seems to correspond to the suicide process known as apoptosis since an early degradation of DNA into oligonucleosome-size fragments could be observed after removal of the growth factor. When present, PDBu inhibits both the activation of the endonuclease and the development of the cell death process in CTLL-2 cells and ConA-blasts deprived of IL-2. Taken together, our results suggest that the tumor promoters phorbol esters inactivate in T cells the mechanism of cell elimination triggered by IL-2 deprivation and may help to explain why transformation of T cells decreases or even abolishes their requirements of IL-2 for survival and growth.     

Relationship between a 47-kDa cytoplasmic membrane polypeptide and nitrate transport in Anacystis nidulans

The polypeptide composition of cytoplasmic membranes of the cyanobacterium Anacystis nidulans changes in response to variations in the nitrogen source available to the cells, differing specifically in the amount of a polypeptide of 47-kDa molecular mass. Synthesis of the polypeptide and expression of nitrate transport activity are repressed by ammonium. Transfer of ammonium-grown cells to a medium containing nitrate as the sole nitrogen source results in parallel development of the 47-kDa polypeptide and nitrate transport activity of the cells. These results suggest the involvement of the 47-kDa cytoplasmic membrane polypeptide in nitrate transport by A. nidulans.     

Inhibition of red cell Ca2+-dependent K+ channels by snake venoms

We have investigated the effects of several snake venoms on the Ca2+-dependent K+ channels of human red cells. A heat-resistant component of the venom of the snake Notechis scutatus irreversibly inhibited Ca2+-dependent K+ transport with a Ki value of 0.1-0.2 micrograms/ml. Metabolic changes of the cells modified the maximal effect of the venom. Binding of the venom required extracellular Ca2+ and was quick, but development of full inhibition required additional time. The effects of the venoms from Notechis scutatus and Leiurus quinquestriatus were additive, suggesting that both venoms act through different mechanisms. Venoms of the snakes Vipera russelli russelli and Oxyuranus scutellatus also inhibited Ca2+-dependent K+ transport with the same characteristics as the Notechis scutatus venom.     

Evidence that replication initiates at only some of the potential origins in each oligomeric form of bovine papillomavirus type 1 DNA.

In a subclone of ID13 mouse fibroblasts latently infected with bovine papillomavirus type 1 (BPV-1) DNA, the viral genome occurred as a mixture of extrachromosomal circular monomers and oligomers. Multiple copies were also associated with the host cell genome, predominantly at a single site in a head-to-tail tandem array. We examined the replicative intermediates of extrachromosomal forms of BPV-1 DNA by using two-dimensional gel electrophoresis. The results obtained indicate that initiation of DNA replication occurred near the center of the EcoRI-BamHI 5.6-kilobase fragment. In some molecules, however, this fragment was replicated from one end to the other by means of a single fork initiated elsewhere. Termination also occurred within this fragment. The EcoRI-BamHI 2.3-kilobase fragment replicated as a DNA molecule containing a termination site for DNA replication and also by means of a single fork traversing the fragment from one end to the other. Thus, replication forks proceeded through these fragments in different manners, apparently depending on whether they were part of a monomer, a dimer, a trimer, or higher oligomers. These observations lead to the conclusion that initiation of DNA replication in BPV-1 DNA takes place at or close to plasmid maintenance sequence 1. From this point, replication proceeds bidirectionally and termination occurs approximately 180 degrees opposite the origin. The results obtained are consistent with one or more replication origins being quiescent in BPV-1 DNA oligomers.     

The caudal spinal cord of coho salmon (Oncorhynchus kisutch): Immunocytochemical evidence of a “caudal serotoninergic system”

Summary The caudal spinal cord of the coho salmon was investigated by means of immunocytochemistry using antisera against serotonin, urotensin I, urotensin II, somatostatin and a urea-extract of bovine Reissner's fiber (AFRU). Populations of serotonin-immunoreactive (IR) neurons were found rostral and dorsal to the urophysis in close spatial association with caudal secretory neurons. Thick, smooth serotonin-IR processes extended toward the external surface of the spinal cord where they displayed conspicuous terminal dilatations. Thin, beaded serotonin-IR fibers appeared to innervate populations of caudal secretory and somatostatin-IR cerebrospinal fluid-contacting neurons. Most caudal neurosecretory cells displayed both urotensin I and urotensin II immunoreactivities; only a minority reacted exclusively with either urotensin I or urotensin II antisera. Urotensin II-IR and somatostatin-IR cerebrospinal fluid (CSF)-contacting neurons were found as an integral component of the central canal wall in the caudal spinal cord and filum terminale; their dendritic processes appeared to contact Reissner's fiber, which displayed a weak AFRU-immunoreactivity while inside the central canal, but became strongly reactive in the interior of the terminal ventricle as it formed the massa caudalis. The distribution of serotoninergic processes points to a regulatory role in the function of caudal secretory and CSF-contacting neurons and to a putative serotonin release into the subarachnoid space and/or meningeal vasculature. It is also suggested that the CSF-contacting neurons of the central canal may participate in a feedback mechanism controlling the secretory activity of the subcommissural organ.Supported by Grant A/1095-1 from the International Foundation for Science, Sweden, to C.Y.; Grant I/63-476 from Volkswagen-Stiftung to E.R.; and Grant S-85-39 from the Dirección de Investigaciones, Universidad Austral de Chile