Big flies, small repeats: the "Thr-Gly" region of the period gene in Diptera

The region of the clock gene period (per) that encodes a repetitive tract of threonine-glycine (Thr-Gly) pairs has been compared between Dipteran species both within and outside the Drosophilidae. All the non- Drosophilidae sequences in this region are short and present a remarkably stable picture compared to the Drosophilidae, in which the region is much larger and extremely variable, both in size and composition. The accelerated evolution in the repetitive region of the Drosophilidae appears to be mainly due to an expansion of two ancestral repeats, one encoding a Thr-Gly dipeptide and the other a pentapeptide rich in serine, glycine, and asparagine or threonine. In some drosophilids the expansion involves a duplication of the pentapeptide sequence, but in Drosophila pseudoobscura both the dipeptide and the pentapeptide repeats are present in larger numbers. In the nondrosophilids, however, the pentapeptide sequence is represented by one copy and the dipeptide by two copies. These observations fulfill some of the predictions of recent theoretical models that have simulated the evolution of repetitive sequences.      

Predominant T cell receptor gene elements in TNP-specific cytotoxic T cells.

H-2b class I-restricted, TNP-specific CTL clones were obtained by limiting dilution cloning of either short term polyclonal CTL lines or spleen cells of TNP-immunized mice directly ex vivo. Sequence analyses of mRNA coding for TCR alpha- and beta-chains of 11 clones derived from CTL lines from individual C57BL/6 mice revealed that all of them expressed unique but clearly nonrandom receptor structures. Five alpha-chains (45%) employed V alpha 10 gene elements, and four of those (36%) were associated with J beta 2.6-expressing beta-chains. The alpha-chains from these four TCR, moreover, contained an acidic amino acid in position 93 of their N or J region-determined sequences. Clones isolated directly from spleen cells carried these types of receptors at lower frequency, 27% V alpha 10 and 19% J beta 2.6, indicating that bulk in vitro cultivation on Ag leads to selection for these particular receptors. However, even in TNP-specific CTL cloned directly ex vivo, V alpha 10 usage was increased about fivefold over that in Ag-independently activated T cells in H-2b mice (4 to 5%). The selection for V alpha 10/J beta 2.6-expressing cells was obtained repeatedly in other TNP-specific CTL lines from C57BL/6 mice but not in FITC-specific CTL from the same strain or in TNP-specific CTL lines from B10.BR (H-2k) or B10.D2 (H-2d) mice. We conclude from this (a) that the selection for V alpha 10/J beta 2.6+ T cells is driven by the complementarity of these receptors to a combination of TNP and MHC epitopes and (b) that predominant receptor structures reflect the existence of a surprisingly limited number of "T cell-relevant" hapten determinants on the surface of covalently TNP-modified cells.     

Nano- and picoplankton growth and production in the Bay of Villefranche sur Mer (N.W. Mediterranean)

Plankton production in the Bay of Villefranche was relatively constant during March and April 1986 but the particle size at which the production occurred was more variable. At the beginning of the study, production was dominated by the larger (ca. 6 m) flagellates but towards the end it was more or less equally divided between the nano- and picoplankton. There were considerable differences in the estimates of population growth rates, depending on the methods used, but on average the population doubling times were close to 12 hours for autotrophs and 24 hours for heterotrophs. As autotrophs do not grow during the night, each population was therefore doubling once per day. It seemed that each of the nanoor picoplankton populations could adversely affect the growth of the others. This could be either by simple predation or by some form of inhibition. Although nutrient levels in the bay were uniformly low, the addition of nutrients did not always stimulate algal growth. The plankton populations seemed to be both in a state of equilibrium and intense ecological competition.     

Marinobacter hydrocarbonoclasticus gen. nov., sp. nov., a new, extremely halotolerant, hydrocarbon-degrading marine bacterium.

On the basis of phenotypical characteristics and analysis of 16S rRNA sequence, a new species belonging to a new genus is described, and the name Marinobacter hydrocarbonoclasticus is proposed. This organism, isolated from Mediterranean seawater near a petroleum refinery, is a gram-negative, aerobic, rod-shaped bacterium. It grows at NaCl concentrations of 0.08 to 3.5 M and uses various hydrocarbons as the sole source of carbon and energy. Its DNA has a guanine-plus-cytosine content of 52.7 mol%. The 16S rRNA analysis shows a clear affiliation between M. hydrocarbonoclasticus and the gamma group of the phylum Proteobacteria. A close phylogenetic relationship appears among the species Marinomonas vaga, Oceanospirillum linum, Halomonas elongata, and Pseudomonas aeruginosa. Because of the impossibility of finding a single most closely related species, we suggest that this bacterium be assigned to a new genus, at least temporarily. The possibility of a revision of this status when new data appear is, however, not excluded. The type strain is M. hydrocarbonoclasticus SP.17 (= ATCC 49840).     

Synthetic peptides anchor T cell-specific TNP epitopes to MHC antigens.

Several TNP-specific, H-2Kb-restricted mouse CTL clones were identified which specifically lysed target cells in the presence of tryptic digests of TNP-modified BSA. Glutaraldehyde fixation of cells revealed that the tryptic fragments did not require further cellular processing. Chromatographic fractionation of digested TNP-BSA identified the peptide TNP-BSA222-231, containing a TNP-modified lysine at BSA position 227, as the antigenic entity. The corresponding synthetic peptide was immunologically cross-reactive with the digest. All clones reactive with TNP-BSA222-231 cross-reacted with a similar peptide from mouse serum albumin (TNP-MSA126-135), favoring the assumption that TNP-BSA222-231 represents an artificial determinant, cross-reacting with some as yet unidentified, TNP-modified, Kb-associated self-peptides. Some of our clones also cross-reacted with tryptic digests of TNP-OVA or TNP-keyhole limpet hemocyanin. We interpret these findings to indicate that 1) a significant proportion of hapten (TNP) determinants for T cells are anchored to MHC via peptides; and 2) the amino acid sequence of these peptides may only partly define the specificity of the T cell-relevant hapten epitope, implying a particularly repetitive nature of these determinants. The production of T cell-antigenic hapten-peptide conjugates will hopefully open new roads to study immune responses to environmental allergens.     

Comparison of rat and guinea pig as sources of the S9 fraction in the salmonella/mammalian microsome mutagenicity test

A highly significant enhancement of mutagenicity occurs with 11 polycyclic aromatic hydrocarbons when 3-methylcholanthrene-induced guinea pig liver S9 is substituted for Aroclor-induced rat liver S9 in the Ames test. The use of MC-induced guinea pig liver S9 is particularly valuable for detecting the weak mutagenicity of benz[c]acridine, which is barely positive in a standard Ames assay. However, anthracene and phenanthrene, which are generally considered not to be carcinogens, remain non-mutagenic for strain TA100. This enhancement of mutagenicity does not correlate with arylhydrocarbon hydroxylase activities of the various liver preparations and does not apply to certain other non-PAH mutagens, including β-naphthylamine, aflatoxin B₁ and 4-dimethylaminoazobenzene.