Conserved sequences in both coding and 5'' flanking regions of mammalian opal suppressor tRNA genes.

The rabbit genome encodes an opal suppressor tRNA gene. The coding region is strictly conserved between the rabbit gene and the corresponding gene in the human genome. The rabbit opal suppressor gene contains the consensus sequence in the 3' internal control region but like the human and chicken genes, the rabbit 5' internal control region contains two additional nucleotides. The 5' flanking sequences of the rabbit and the human opal suppressor genes contain extensive regions of homology. A subset of these homologies is also present 5' to the chicken opal suppressor gene. Both the rabbit and the human genomes also encode a pseudogene. That of the rabbit lacks the 3' half of the coding region. Neither pseudogene has homologous regions to the 5' flanking regions of the genes. The presence of 5' homologies flanking only the transcribed genes and not the pseudogenes suggests that these regions may be regulatory control elements specifically involved in the expression of the eukaryotic opal suppressor gene. Moreover the strict conservation of coding sequences indicates functional importance for the opal suppressor tRNA genes.     

Taxonomy and distribution of Chaptalia dentata and C. Albicans (Asteraceae: Mutisieae)

Chaptalia dentata (L.) Cass. andC. albicans (Sw.) Vent. ex Steudel incorrectly have been recognized as conspecific in recent treatments. Although they are vegetatively similar, they differ in features of the flowers and fruits—especially the mature achenes. Both species occur in the Bahamas and the Greater Antilles of the West Indies:Chaptalia dentata is endemic to that area, absent only from Jamaica;C. albicans is more widespread, as it occurs in Jamaica as well as in scattered localities on the American mainland—southern Florida, various localities in Belize, Honduras, and Guatemala, and the Mexican states of Veracruz, San Luis Potosí, Chiapas, and Yucatán.     

Lymphokine regulation of human lymphocyte proliferation: Formation of resting G0 cells by removal of interteukin 2 in cultures of proliferating T lymphocytes

The question of whether lymphocytes which have once been activated and have completed one or several cell cycle(s) can return to the G₀ phase and stay ready for a new activation (G₀-G₁ transition), rather than simply die, was investigated. To do so interleukin 2 (IL-2) was removed from cultures of continuously proliferating human T lymphocytes and the formation of resting (G₀) cells was measured. Kinetic analyses in freshly prepared peripheral blood lymphocytes (PBL) revealed that the onset of detectable RNA synthesis and the appearance of structures binding the anti-Tac antibody occurred simultaneously. This allowed the expansion of the definition of G₀ T lymphocytes as cells having a low RNA (and DNA) content, and no Tac antigen. When cultured human T cells proliferating continuously by means of IL-2 were characterized in terms of their distribution in the cell cycle, 7 days after the initial PHA stimulation, it could be demonstrated that very few cells were in the G₀ phase, supporting the concept of direct S/G₂/M-G₁ transition. However, when IL-2 was removed from the cultures, the [³H]thymidine incorporation per 10⁴ cells and correspondingly the number of cells in the S/G₂/M and G₁ phases were reduced drastically and during the following 72-hr period, the number of G₀ cells increased markedly. Restimulation of such in vitro formed G₀ cells, under conditions permitting observation of their shift from the G₀ to G₀ phase, demonstrated that most cells could respond normally. Based on these observations, it was concluded that IL-2 not only ensures T-lymphocyte survival and proliferation, but IL-2 starvation induces many continuously proliferating T lymphocytes to stop cycling and to return to the G₀ phase of the cell cycle where they remain functional.     

Glycinebetaine content of halophytes: Improved analysis by liquid chromatography and interpretations of results

The glycinebetaine content of plants can be determined by simple isocratic high performance liquid chromatography. The method is applicable to extracts from a wide range of species and, in most cases, is suitably rapid and specific to be preferable to other methods of analysis. The chromatographic system employed permits accurate and sensitive ultraviolet detection, free of most interferences. Because the principle plant carbohydrates elute well before glycine betaine, preparative ion exchange procedures can be simplified. Twenty-seven species, mostly inland halophytes, were screened by these methods and 13 were found to be glycinebetaine accumulators. On a dry weight basis, the glycinebetaine content of Salicornia europaea L. actually declined with exposure to progressively higher levels of NaCl. When expressed as a proportion of plant organic matter, however, patterns were more typical (up to 7.7% at higher salt concentrations).     

A proton-deuterium exchange study of three types ofDesulfovibrio hydrogenases

Summary Hydrogenases are among the main enzymes involved in bacterial anaerobic corrosion of metals. The study of their mode of action is important for a full comprehension of this phenomenon. The three types ofDesulfovibrio hydrogenases [(Fe), (NiFe), (NiFeSe)] present different patterns in the pH dependence of their activity. The periplasmic enzyme fromDesulfovibrio salexigens and the cytoplasmic enzyme fromDesulfovibrio baculatus both have pH optima at 7.5 for H₂ uptake and 4.0 for H₂ evolution and H⁺–D₂ exchange reaction (measured by membrane-inlet mass-spectrometry). The H₂ to HD ratio at pH above 5.0 is higher than 1.0. The periplasmic hydrogenase fromD. gigas presents the same pH optimum (8.0) for the H⁺–D₂ exchange as for H₂ consumption. In contrast, the enzyme fromD. vulgaris has the highest activity in H₂ production and in the exchange at pH 5.0. Both hydrogenases have a H₂-to-HD ratio below 1.0.     

The relationship between hydrogen metabolism,sulfate reduction and nitrogen fixation in sulfate reducers

Summary Hydrogenase and nitrogenase activities of sulfate-reducing bacteria allow their adaptation to different nutritional habits even under adverse conditions. These exceptional capabilities of adaptation are important factors in the understanding of their predominant role in problems related to anaerobic metal corrosion. Although the D₂–H⁺ exchange reaction indicated thatDesulfovibrio desulfuricans strain Berre-Sol andDesulfovibrio gigas hydrogenases were reversible, the predominant activity in vivo was hydrogen uptake. Hydrogen production was restricted to some particular conditions such as sulfate or nitrogen starvation. Under diazotrophic conditions, a transient hydrogen evolution was followed by uptake when dinitrogen was effectively fixed. In contrast, hydrogen evolution proceeded when acetylene was substituted as the nitrogenase substrate. Hydrogen can thus serve as an electron donor in sulfate reduction and nitrogen metabolism.     

Immunoprecipitation of phytochrome from green Avena by rabbit antisera to phytochrome from etiolated Avena

Thirty-nine antiserum preparations from eight rabbits were screened for their ability to precipitate the immunochemically distinct phytochrome that is obtained from green oat (Avena sativa L.) shoots. The antisera were obtained from rabbits immunized with either proteolytically degraded, but still photoreversible, 60-kDa (kilodalton) phytochrome, or approx. 120-kDa phytochrome, both of which were purified from etiolated oat shoots. The ability of these antisera to precipitate phytochrome from green oats was independent of the size of phytochrome used for immunization. While crude antisera immunoprecipitated as much as 80% of the phytochrome isolated from green oat shoots, antibodies immunopurified from these sera with a column of highly purified, approx. 120-kDa phytochrome from etiolated oats precipitated no more than about 5–10%.Abbreviations kDa kilodalton - mU milliunit     

Direct evidence for the existence of nominal antigen binding sites on T cell surface Ti alpha-beta heterodimers of MHC-restricted T cell clones

The binding of nominal antigen to Ti alpha-beta heterodimers on MHC-restricted human T cell clones specific for fluorescein-5-isothiocyanate (FL) was detected by flow cytometry and affinity chromatography. The FL-Ti interaction is of physiologic significance, since T cell activation is induced by cross-linked arrays of FL in the absence of the specific MHC recognition. High antigen valence is required to achieve stable binding to cells and subsequent activation, which is consistent with estimated Ti-FL association constants of less than 3 X 10(5) l/mol. In addition to providing direct evidence that the Ti alpha-beta heterodimer is the receptor for antigen, these data suggest that nominal antigen binding sites exist on the Ti molecules of at least some MHC-restricted clones.     

Isotretinoin teratogenicity in mouse whole embryo culture

Recent clinical observations strongly suggest that isotretinoin [13-cis-retinoic acid (cis RA)] is a human teratogen causing primarily heart and craniofacial malformations including ear and palatal defects. The purpose of the present study was to determine if cis RA could induce similar craniofacial malformations in mouse embryo culture. Day 8 CD-1 mouse embryos were cultured for 48 hours in rat serum in the presence or absence of various concentrations of cis RA dissolved in DMSO. DMSO by itself had no effect on embryonic development; however, cis RA at 2 X 10(-5) M (6 micrograms/ml) was clearly toxic. At 2 X 10(-6) M cis RA, growth retardation was minimal, and approximately one-third of the embryos exhibited very specific defects including a dramatic reduction in the size of the first and second visceral arches, which eventually give rise to the maxilla, mandible, and ear. Similar observations were also made with 4-oxo-13-cis RA, which is a major metabolite of cis RA in the mouse and human. These malformations would be expected to result in defects similar to those observed in the human, and preliminary observations suggest these defects are due to cis RA-induced inhibition of cranial neural crest cell migration. Using day-10 mouse embryos cultured for 48 hours in Waymouth's medium containing 50% fetal calf serum, we observed that cis RA at 2 X 10(-5) M produced a high percentage of embryos with limb defects and median cleft lip. Our results demonstrate that labeled cis RA enters the tissues of the embryo both in vivo and in vitro. Cis RA inhibited proliferation of the frontonasal mesenchyme cells in primary culture with 31% inhibition occurring at 2 X 10(-5) M cis RA.