A mRNA-based thermosensor controls expression of rhizobial heat shock genes.

Expression of several heat shock operons, mainly coding for small heat shock proteins, is under the control of ROSE (repression of heat shock gene expression) in various rhizobial species. This negatively cis-acting element confers temperature control by preventing expression at physiological temperatures. We provide evidence that ROSE-mediated regulation occurs at the post-transcriptional level. A detailed mutational analysis of ROSE(1)-hspA translationally fused to lacZ revealed that its highly conserved 3'-half is required for repression at normal temperatures (30 degrees C). The mRNA in this region is predicted to form an extended secondary structure that looks very similar in all 15 known ROSE elements. Nucleotides involved in base pairing are strongly conserved, whereas nucleotides in loop regions are more divergent. Base substitutions leading to derepression of the lacZ fusion at 30 degrees C exclusively resided in potential stem structures. Optimised base pairing by elimination of a bulged residue and by introduction of complementary nucleotides in internal loops resulted in ROSE elements that were tightly repressed not only at normal but also at heat shock temperatures. We propose a model in which the temperature-regulated secondary structure of ROSE mRNA influences heat shock gene expression by controlling ribosome access to the ribosome-binding site.

Rescue of gamma2 subunit-deficient mice by transgenic overexpression of the GABAA receptor gamma2S or gamma2L subunit isoforms.

The gamma2 subunit is an important functional determinant of GABAA receptors and is essential for formation of high-affinity benzodiazepine binding sites and for synaptic clustering of major GABAA receptor subtypes along with gephyrin. There are two splice variants of the gamma2 subunit, gamma2 short (gamma2S) and gamma2 long (gamma2L), the latter carrying in the cytoplasmic domain an additional eight amino acids with a putative phosphorylation site. Here, we show that transgenic mice expressing either the gamma2S or gamma2L subunit on a gamma2 subunit-deficient background are phenotypically indistinguishable from wild-type. They express nearly normal levels of gamma2 subunit protein and [3H]flumazenil binding sites. Likewise, the distribution, number and size of GABAA receptor clusters colocalized with gephyrin are similar to wild-type in both juvenile and adult mice. Our results indicate that the two gamma2 subunit splice variants can substitute for each other and fulfil the basic functions of GABAA receptors, allowing in vivo studies that address isoform-specific roles in phosphorylation-dependent regulatory mechanisms.

Glia cell stimulating factor (GSF): a new lymphokine. Part 1. Cellular sources and partial purification of murine GSF, role of cytoskeleton and protein synthesis in its production.

The effect of activated-lymphocyte supernatant on glia cells was investigated. When treated in vitro with Concanavalin A (ConA), murine spleen cells released a soluble product, termed glia cell stimulating factor (GSF), which stimulated RNA and DNA synthesis in cultured murine glia cells. Furthermore, GSF appeared to promote the maturation of undifferentiated glia cells to astrocytes having a high content of glial fibrillary acidic protein. GSF secretion occurred after a lag period of 16 hours and proceeded at a constant rate for more than 48 hours. This GSF produced by ConA-stimulated murine lymphocytes has an apparent molecular weight between 60,000 and 80,000. Antigenic stimulation of primed lymph node cells with BGG resulted in a similar GSF production. Cellular sources of mitogen-induced GSF were investigated by using isolated lymphoid populations. GSF release by ConA-activated pure T-lymphocytes reconstituted with peritoneal macrophages was equivalent to that of unseparated spleen cells, whereas GSF production by T-lymphocytes alone was low. Macrophages alone did not elaborate detectable levels of GSF. GSF was also secreted by enriched -B-lymphocytes populations stimulated by Protein A. Formation of GSF was suppressed when cytochalasin B or cyclo-heximide was added to the cultures, while colchicine failed to have any effect. DNA synthesis is not required for GSF production as determined by resistence to treatment with mitomycin C. The data indicate that the GSF production and secretion mechanism is much like that described for other lymphokines.

Involvement of cyclic AMP in the regulations of lymphokine induced glia cell stimulation.

T and B lymphocytes of human or murine origin were found to secrete a factor which increases the DNA and RNA synthesis of cultured glia cells. This factor, termed glia cell stimulating factor (GSF), is released upon stimulation of such immune cells by mitogen or antigen qualifying it as a lymphokine. In this communication we report on the role of cyclic AMP (cAMP) in regulating the effect of GSF on glia cells. Prostaglandin E1 (PGE1), isoproterenol and theophylline were effective in suppressing the GSF-induced increase of the glia cell proliferation. No inhibition of DNA synthesis and no decrease in cell number was observed when testing these substances on glia cells not being activated by GSF. The drugs were found to induce an increase in cAMP concentrations of glia cells. A partial desensitization of the glia cells to these drug induced elevations of cAMP was detected after pretreatment of the glia cell cultures with GSF. It is suggested that stimulated lymphocytes not only release GSF but also low molecular weight proteins such as PGE1 which regulate the effects of GSF on glia cells by activating their adenylate cyclase.