Satellite DNA repeat sequence variation is low in three species of burying beetles in the genus Nicrophorus (Coleoptera: Silphidae)

Three satellite DNA families were identified in three species of burying beetles, Nicrophorus orbicollis, N. marginatus, and N. americanus. Southern hybridization and nucleotide sequence analysis of individual randomly cloned repeats shows that these satellite DNA families are highly abundant in the genome, are composed of unique repeats, and are species-specific. The repeats do not have identifiable core elements or substructures that are similar in all three families, and most interspecific sequence similarity is confined to homopolymeric runs of A and T. Satellite DNA from N. marginatus and N. americanus show single-base-pair indels among repeats, but single-nucleotide substitutions characterize most of the repeat variability. Although the repeat units are of similar lengths (342, 350, and 354 bp) and A + T composition (65%, 71%, and 71%, respectively), the average nucleotide divergence among sequenced repeats is very low (0.18%, 1.22%, and 0.71%, respectively). Transition/transversion ratios from the consensus sequence are 0.20, 0.69, and 0.70, respectively.      

Single calcium channels and their inactivation

Inactivation of single Ca channels in snail neurons was examined to test the idea that entering Ca ions react directly with the channel to produce this effect. Simulations of specific models were used for comparison with the experimental data. The Ca-dependent model predicts time-dependent changes in the single-channel events which were not found experimentally. It is possible that Ca-dependent inactivation is mediated by a Ca-binding protein that is associated with but not part of the channel itself.     

Conformational analysis of cholecystokinin CCK26-33 and related fragments by 1H NMR spectroscopy, fluorescence-transfer measurements, and calculations

The conformational behavior of CCK7, Tyr-Met-Gly-Trp-Met-Asp-Phe-NH2, and CCK8, Asp-Tyr-Met-Gly-Trp-Met-Asp-Phe-NH2, in their sulfated and unsulfated forms, was studied both by 1H NMR spectroscopy in dimethyl-d6 sulfoxide and water and by fluorescence-transfer measurements at pH 7. In neutral conditions, both experimental methods show that these peptides exist preferentially in folded forms with beta and gamma turns around the sequence Gly-Trp-Met-Asp and Met-Asp-Phe-NH2, respectively. The presence of stable folded conformations is supported by through-space effects during the titration of the ionizable groups and by the weak temperature dependency of some amide protons not only in dimethyl sulfoxide but also in water. The folding of the C-terminal part, already shown in CCK5, seems to be a common conformational characteristic in CCK peptides. The N-terminal part of CCK8 presents an equilibrium between beta and gamma turns, whereas this part of the peptide is more flexible in CCK7. The low quantum yield of Tyr and the large mean distance (R = 15 A) between Tyr and Trp, determined by fluorescence-transfer measurements, support the occurrence of folded conformations pushing the aromatic rings far from each other. Interestingly, the introduction of the sulfate group enhances the folding tendency even in aqueous medium. The larger amide temperature dependency and the decrease in the R distance at acidic pH suggest that an intramolecular ionic interaction involving the N-terminal amino group and the beta-carboxyl groups of Asp32 stabilize the folded forms. Metropolis calculations performed on CCK8 support the existence of stable folded conformations closely related to those deduced from experimental data.(ABSTRACT TRUNCATED AT 250 WORDS)     

Zinc as a second messenger of mitogenic induction. Effects on diadenosine tetraphosphate (Ap4A) and DNA synthesis

DNA synthesis and adenosine(5')tetraphosphate(5')adenosine (Ap4A) levels decrease in cells treated with EDTA. The inhibitory effect of EDTA can be reversed with micromolar amounts of ZnCl2. ZnCl2 in micromolar concentrations also inhibits Ap4A hydrolase and stimulates amino acid-dependent Ap4A synthesis, suggesting that Zn2+ is modulating intracellular Ap4A pools. Serum addition to G1-arrested cells enhances uptake of Zn, whereas serum depletion leads to a fivefold decrease of the rates of zinc uptake. These results are discussed by regarding Zn2+ as a putative 'second messenger' of mitogenic induction and Ap4A as a possible 'third messenger' and trigger of DNA synthesis.     

The course of root differentiation from root primordia in poplar stems

Upon rooting of poplar stem cuttiags the total inductive stimulation does not take place, but the individual root primordia maintain a relative independence. This becomes evident by various time parameters of their differentiation. Under experimental conditions, in dormant cuttings from one year individuals of the hybrid I 214 the activation of the first root primordia occurs after 24 h, the pre-emergent development of the roots formed was completed after 72 h. The activated root primordium is divided into two regions. In the distal region with the predominating cell division the root apex with histogens is formed by the action of initials. From peripheral cell layers of the distal region the so-called “Wurzeltasche” develops which covers the root cap. Due to cell elongation in the proximal region the root apex is pushed up towards the stem surface. The beginning differentiation of the connective vascular tissue is a preparative step for the connection of the vascular system of the developing root with the secondary vascular system of the maternal stem. Following the penetration of the root through the peripheral stem tissues this connection is realized with progressing development. In the developed root the protoxylem elements differentiate continuously and acropetally in direct continuity with tracheids of the basal connective region.