Nucleotide sequence and evolution of a mammalian α-Tubulin messenger RNA

Bacterial clones containing complementary DNA sequences specific for rat brain α-tubulin messenger RNA were constructed. One plasmid, pILαTl, contains >95% of the sequences found in the mRNA: the entire coding sequence as well as extensive 5′ and 3′ untranslated sequences. Comparison of the rat amino acid sequence with the known chicken α-tubulin sequence (Valenzuela et al., 1981) reveals the extraordinary evolutionary stability of α-tubulin protein. The presence of only two interspecies amino acid differences within analogous 411 amino acid sequences predicts that amino acid substitutions in this protein are fixed with a unit evolutionary period (Wilson et al., 1977) of 550 million years (i.e. the time required for a 1% difference to arise within a specific protein in two diverging evolutionary lineages). An analysis of the silent nucleotide differences, permissible because of the degeneracy of the genetic code, demonstrates that these might not occur in a random fashion. The high guanine-cytosine bias in silent codon positions within the chicken α-tubulin sequence, previously noted by Valenzuela et al. (1981), is not conserved within the rat sequence. This decrease in guanine-cytosine bias is accompanied by a selective loss of CpG dinucleotides in the rat sequence.     

Role of sugars in nitrate utilization by roots of dwarf bean

Nitrate uptake and in vivo, nitrate reductase activity (NRA) in roots of Phaseolus vulgaris, L. cv. Witte Krombek were measured in nitrogen-depleted plants of varying sugar status, Variation in sugar status was achieved at the start of nitrate nutrition by excision, ringing, darkness or administration of sugars to the root medium. The shape of the apparent induction pattern of nitrate uptake was not influenced by the sugar status of the absorbing tissue. When measured after 6 h of nitrate nutrition (0.1 mol m^?3), steady state nitrate uptake and root NRA were in the order intact>dark>ringed>excised. Exogenous sucrose restored NRA in excised roots to the level of intact plants. The nitrate uptake rate of excised roots, however, was not fully restored by sucrose (0.03–300 mol m^?3). When plants were decapitated after an 18 h NO₃^? pretreatment, the net uptake rate declined gradually to become negative after three hours. This decline was slowed down by exogenous fructose, whilst glucose rapidly (sometimes within 5 min) stimulated NG^?₃ uptake. Presumably due to a difference in NO₃^? due to a difference in NO₃^? uptake, the NRA of excised roots was also higher in the presence of glucose than in the presence of fructose after 6 h of nitrate nutrition. The sugar-stimulation of, oxygen consumption as well as the release of ¹⁴CO₂ from freshly absorbed (U-¹⁴C) sugar was the same for glucose and fructose. Therefore, we propose a glucose-specific effect on NO₃^? uptake that is due to the presence of glucose rather than to its utilization in root respiration. A differential glucose-fructose effect on nitrate reductase activity independent of the effect on NO₃^? uptake was not indicated. A constant level of NRA occurred in roots of NO₃^? induced plants. Removal of nutrient nitrate from these plants caused an exponential NRA decay with an approximate half-life of 12 h in intact plants and 5.5 h in excised roots. The latter value was also found in roots that were excised in the presence of nitrate, indicating that the sugar status primarily determines the apparent rate of nitrate reductase decay in excised roots.     

Disproportionate rDNA replication does occur in diploid tissue in Drosophila hydei

Summary The rDNA content in Drosophila hydei has been compared in wild-type and in two translocation genotypes possessing only one nucleolus organizer. In highly polyploid salivary glands where rDNA is underreplicated, an independent polytenization of the rDNA occurs resulting in about the same rDNA level in each genotype independently of the number of nucleolous organizers present in the genome. Thus, the situation in the salivary glands of D. hydei is similar to that in D. melanogaster (Spear and Gall 1973).In tetraploid thoracic muscle where rDNA is not underreplicated, the rDNA percentage in the two translocation genotypes is also considerably increased, although the wild-type level is not completely attained. This result shows that rDNA replication is independently controlled even in a non-underreplicating tissue.In larval diploid brain the situation in the two translocation stocks is dissimilar: in one genotype the rDNA content remains unaltered whereas in the other it is increased. This demonstrates for the first time that a gene compensation does occur in a diploid tissue.Supported by a grant from the Deutsche Forschungsgemeinschaft (Ku 282/7)     

Human plasma-derived immunosuppressive factors having anti-lymphoma activity

Summary Extraction of Cohn IV-1, an -globulin enriched fraction of human plasma, with a high-salt, low-pH solution, followed by sequential ultrafiltration steps yielded an immunosuppressive preparation (UM05R) of mol.wt. 500–10,000. UM05R inhibited antibody formation in the mouse in vivo and transformation in vitro of lymphocytes treated with either T-or B-cell stimulants. Suppression of lymphocyte transformation, indicated by inhibition of ³H-thymidine incorporation into DNA, was confirmed by inhibition of blast cell formation. From dose-response curves the UM05R concentration to produce 50% suppression of lymphocyte blast transformation was 15–50 g protein/ml. Selectivity for lymphoid cells was suggested by growth inhibition in vitro of L1210 and P1798 leukemias but not murine neuroblastoma or human fetal fibroblasts. This observation also rules out the presence of an agent which is broadly cytotoxic. Fractionation of UM05R on Sephadex G-25 in 10% acetic acid yielded an early-emerging fraction, mol. wt. 5,000–10,000, containing B-cell inhibitor, and a late fraction, mol. wt. 1,400, inhibitory for both T- and B-cell transformation and growth of L1210. The inhibitory activity for B cells was removed from the other two activities by 5% trichloroacetic acid (TCA). The possibility is raised that the inhibitory activity for T cells and L1210 may reside in the same molecule. Sensitivity of the early-emerging B-cell inhibitor to carboxypeptidase B suggests that it is a polypeptide, but resistance of the T-cell inhibitor to various treatments leaves its nature uncertain. The properties of these factors suggest consideration of them as lymphocyte chalones occurring in plasma complexed to high-molecular-weight components.     

Comparison of the steroidogenic and melanotropic activities of corticotropin, alpha-melanotropin and analogs with their lipolytic activities in rat and rabbit adipocytes.

The ability of alpha-melanotropin and a series of synthetic peptides related to adrenocorticotropin (ACTH) to stimulate steroidogenesis in isolated rat adrenal cells, melanin dispersion in frog melanophores and lipolysis in rat and rabbit fat cells have been studied. It was found that the steroidogenic activity closely paralleled the lipolytic activity of these peptides in rat fat cells, whereas the melanocyte stimulating activity paralleled the lipolytic activity in rabbit fat cells. These results indicate that the structural requirements for stimulating steroidogenesis in isolated rat adrenal cells and lipolysis in isolated rat fat cells are quite similar. The structural features required for eliciting lipolysis in rabbit fat cells appear to be very similar to those necessary for stimulating frog melanophores. The possibility that regulation of lipid metabolism in the rabbit may be a new function acquired by melanotropin is discussed.     

Characterization of polysomes from Xenopus liver synthesizing vitellogenin and translation of vitellogenin and albumin messenger RNA's in vitro.

1. Conditions are described for the isolation of polysomes from the liver of Xenopus laevis. The method involves homogenization of liver in 0.2 M Tris-HCl pH 8.5, treatment with 2% Triton X-100 and subsequent sucrose density gradient fractionation of polysomes from a 10000 X g supernatant. 2. Vitellogenin synthesis was induced in male Xenopus liver by oestradiol treatment. Polysomes were isolated and vitellogenin-synthesizing polysomes characterized by their association with monospecific 125 I-labelled rabbit anti-vitellogenin antibody and by reaction with rabbit anti-vitellogenin immunoglobulins followed by indirect immunoprecipitation with goat anti-rabbit antibody. 3. Changes in liver polysome content following oestrogen treatment of male Xenopus are correlated with the appearance of vitellogenin synthesis using an organ culture assay. 4. RNA extracted from livers of oestradiol-treated male Xenopus and from purified polysomes is shown to code for the synthesis of vitellogenin-specific immunoprecipitable polypeptides in a rabbit reticulocyte cell-free protein-synthesizing system, a major component having a molecular weight of 210000. Xanopus liver RNA is also shown to code for the synthesis of an albumin-specific immunoprecipitable polypeptide of 74000 molecular-weight which coelectrophoresed with Xenopus albumin.     

Acetyl groups in cell-wall preparations from higher plants

O-Acetyl groups were detected by i.r. spectroscopy in cell-wall preparations from grasses and other higher plants and their presence was confirmed chemically. The amounts present are likely to influence both the physical state of the cell-wall polysaccharides and also their digestion by enzymes.