Elevation of the heat resistance of Salmonella typhimurium by sublethal heat shock

The survival of Salmonella typhimurium after a standard heat challenge at 55°C for 25 min increased by several orders of magnitude when cells grown at 37°C were pre-incubated at 42°, 45° or 48°C before heating at the higher temperature. Heat resistance increased rapidly after the temperature shift, reaching near maximum levels within 30 min. Elevated heat resistance persisted for at least 10 h. Preincubation of cells at 48°C for 30 min increased their resistance to subsequent heating at 50°, 52°, 55°, 57° or 59°C. Survival curves of resistant cells were curvilinear. Estimated times for a '7D' inactivation increased by 2.6- to 20-fold compared with cells not pre-incubated before heat challenge.     

Structural organization of the human kininogen gene and a model for its evolution

The entire human kininogen gene has been isolated as a set of overlapping genomic DNA fragments, and the 11 exons encompassing approximately 27 kilobase pairs have been mapped by restriction enzyme analysis and nucleotide sequence determination. The nine 5'-terminal exons encode the 5'-untranslated region and the protein-coding region for the signal peptide and the heavy chain, which are common for high molecular weight (HMW) and low molecular weight (LMW) prekininogen mRNAs. Exon 10 consists of the common sequence for bradykinin and the immediately following unique sequence for HMW prekininogen mRNA. Exon 11 is then located following a 90-nucleotide sequence downstream from exon 10 and precisely specifies the sequence unique to LMW prekininogen mRNA. This, together with the hybridization analysis of total human cellular DNA, leads us to conclude that human HMW and LMW prekininogen mRNAs are produced from a single gene as a consequence of alternative RNA processing events. The structural analysis of the kininogen gene also shows that each of the nine 5'-terminal exons discretely specifies the nine protein domains observed in the amino-terminal portion of the kininogens. Furthermore, these nine genetic domains can be characterized by a thrice repeated pattern of three genetic segments, and two sets of these three domains, encompassing exons 3-5 and exons 6-8, are most closely related to each other. Therefore, we have proposed two successive duplication mechanisms as a model for the generation of the structure of the kininogen gene.     

Characterization of the env gene and long terminal repeat of molecularly cloned Friend mink cell focus-inducing virus DNA

The highly oncogenic erythroleukemia-inducing Friend mink cell focus-inducing (MCF) virus was molecularly cloned in phage lambda gtWES.lambda B, and the DNA sequences of the env gene and the long terminal repeat were determined. The nucleotide sequences of Friend MCF virus and Friend spleen focus-forming virus were quite homologous, supporting the hypothesis that Friend spleen focus-forming virus might be generated via Friend MCF virus from an ecotropic Friend virus mainly by some deletions. Despite their different pathogenicity, the nucleotide sequences of the env gene of Friend MCF virus and Moloney MCF virus were quite homologous, suggesting that the putative parent sequence for the generation of both MCF viruses and the recombinational mechanism for their generation might be the same. We compare the amino acid sequences in lymphoid leukemia-inducing ecotropic Moloney virus and Moloney MCF virus, and erythroblastic leukemia-inducing ecotropic Friend virus, Friend-MCF virus, and Friend spleen focus-forming virus. The Friend MCF virus long terminal repeat was found to be 550 base pairs long. This contained two copies of the 39-base-pair tandem repeat, whereas the spleen focus-forming virus genome contained a single copy of the same sequence.     

Synaptosomal Calcium Metabolism During Hypoxia and 3,4-Diaminopyridine Treatment

A decline in the calcium-dependent release of neurotransmitters appears to underlie the decreased neuronal function that accompanies reduced oxygen tensions (hypoxia). To determine if alterations in calcium uptake are primary to these changes, synaptosomal calcium uptake was measured in the presence of 100%, 2.5%, or 0% oxygen. Calcium uptake declined 60.2 +/- 0.1 and 82.4 +/- 2.5% with 2.5% and 0% when compared with 100% oxygen, respectively. 3,4-Diaminopyridine stimulated calcium uptake by synaptosomes when they were incubated in low-potassium media. It also diminished the hypoxic-induced decline in calcium uptake to 30.6 +/- 3.1 and 33.5 +/- 3.1% with 2.5% and 0% oxygen, respectively. External binding to the synaptosomal plasma membrane declined to 29.2 +/- 0.3 or 11.8 +/- 0.9% when the oxygen tension was reduced to 2.5% or 0% oxygen. 3,4-Diaminopyridine increased this superficial binding from 111.7 +/- 0.3 to 86.5 +/- 0.9 or 23.4 +/- 0.9% with 100%, 2.5%, or 0% oxygen when compared with 100% oxygen without 3,4-diaminopyridine, respectively. Thus, the decline in neuronal processing that accompanies acute hypoxia may be due to altered calcium homeostasis, which diminishes neurotransmitter release.     

Characterization of an antigen-specific suppressive factor derived from a cloned suppressor effector T cell line

A cloned effector-type suppressor T cell line, 3D10, which is known to suppress the antibody response against dinitrophenylated keyhole limpet hemocyanin (KLH), produced a soluble KLH-specific factor (TsF) that can replace the function of parental T cell clones. High activity of TsF was released spontaneously into the culture supernatant when cultured in interleukin 2 (IL 2)-containing medium, requiring no antigenic stimulation. The culture supernatant of 3D10 was also capable of inhibiting the KLH-induced proliferative response of primed T cells in an antigen-specific manner. The direct target of TsF was found to be Lyt-1+2- T cells undergoing an early stage of antigen-specific proliferation. TsF was antigen binding but lacked any other serologic markers such as I-J and immunoglobulin heavy chain-linked allotypic determinants on T cells. No genetic restriction was found in its action on allogeneic T cells. The production of IL 2 in proliferative T cells by antigenic stimulation was not inhibited by TsF. These results indicate that the TsF described here is the legitimate mediator produced by the effector-type suppressor T cell that suppresses the antigen-specific responses of Lyt-1+2- T cells. The m.w. of TsF was approximately 75,000.