Novel changes in the plasma membrane and cortical cytoplasm during wound-induced contraction in a giant-celled green alga

Summary Changes in the plasma membrane surface and in the cortical cytoplasm during wound healing in giant green algal cells ofErnodesmis verticillata (Kützing) Brgesen were followed using scanning and transmission electron microscopy. Microvillus-like structures that contain cytoplasmic and cytoskeletal constituents were observed emanating from the surface of the plasma membrane at the retracting/cut end of wounded cells. These delicate structures seem to be remnants of cell wall-plasmalemma connections that draw out the plasma membrane and cortical components from the contracting cytoplasm as it pulls away from the cell wall. Most of these connections break during wound healing and, when contraction stops, the microvillus-like protrusions become progressively shorter. In cells treated with a calmodulin antagonist (W-7), a number of distinctive bodies accumulate that are of unknown composition, are oblong in shape, and have a diameter slightly smaller than the protoplasmic protrusions. Ultrastructural and other data indicate that these bodies result from retrieved constituents of the plasma-membrane protrusions, as they do not accumulate in unwounded drugtreated cells or in cells treated in W-5. These findings suggest that the protoplasmic protrusions accumulate membrane and cytoplasmic components that are retrieved and recycled during wound healing inErnodesmis by a novel mechanism. The combined plasma membrane surfaces of the microvillus-like protrusions may help to account for the drastic decrease in surface area that occurs during wound healing.Abbreviations SEM scanning electron microscopy - TEM transmission electron microscopy - W-7 N-[6-aminohexyl]-5-chloro-1-naph-thalenesulfonamide - W-5 N-[6-aminohexyl]-1-naphthalenesulfonamide     

Building proteins from C alpha coordinates using the dihedral probability grid Monte Carlo method.

Dihedral probability grid Monte Carlo (DPG-MC) is a general-purpose method of conformational sampling that can be applied to many problems in peptide and protein modeling. Here we present the DPG-MC method and apply it to predicting complete protein structures from C alpha coordinates. This is useful in such endeavors as homology modeling, protein structure prediction from lattice simulations, or fitting protein structures to X-ray crystallographic data. It also serves as an example of how DPG-MC can be applied to systems with geometric constraints. The conformational propensities for individual residues are used to guide conformational searches as the protein is built from the amino-terminus to the carboxyl-terminus. Results for a number of proteins show that both the backbone and side chain can be accurately modeled using DPG-MC. Backbone atoms are generally predicted with RMS errors of about 0.5 A (compared to X-ray crystal structure coordinates) and all atoms are predicted to an RMS error of 1.7 A or better.     

Magnesium-induced inner membrane aggregation in heart mitochondria: prevention and reversal by carboxyatractyloside and bongkrekic acid

Mg(2+) at an optimal concentration of 2mM (ph 6.5) induces large increases (up to 30 percent) in the optical density of bovine heart mitochondria incubated under conditions of low ionic strength (< approx. 0.01). The increases are associated with aggregation (sticking together) of the inner membranes and are little affected by changes in the energy status of the mitochondria. Virtually all of a number of other polyvalent cations tested and Ag(+) induce increases in mitochondrial optical density similar to those induced by Mg(2+), their approximate order of concentration effectiveness in respect to Mg(2+) being: La(3+) > Pb(2+) = Cu(2+) > Cd(2+) > Zn(2+) > Ag(+) > Mn(2+) > Ca(2+) > Mg(2+). With the exception of Mg(2+), all of these cations appear to induce swelling of the mitochondria concomitant with inner membrane aggregation. The inhibitors of the adenine nucleotide transport reaction carboxyatratyloside and bongkrekic acid are capable of preventing and reversing Mg(2+)-induced aggregation at the same low concentration required for complete inhibition of phosphorylating respiration, suggesting that they inhibit the aggregation by binding to the adenine nucleotide carrier. The findings are interpreted to indicate (a) that the inner mitochondrial membrane is normally prevented from aggregating by virtue of its net negative outer surface change, (b) that the cations induce the membrane to aggregate by binding at its outer surface, decreasing the net negative charge, and (c) that carboxyatractyloside and bongkrekic acid inhibit the aggregation by binding to the outer surface of the membrane, increasing the net negative charge.     

Evidence on the conformation of HeLa-cell 5.8S ribosomal ribonucleic acid from the reaction of specific cytidine residues with sodium bisulphite.

The reaction of HeLa-cell 5.8S rRNA with NaHSO3 under conditions in which exposed cytidine residues are deaminated to uridine was studied. It was possible to estimate the reactivities of most of the 46 cytidine residues in the nucleotide sequence by comparing 'fingerprints' of the bisulphite-treated RNA with those of untreated RNA. The findings were consistent with the main features of the secondary-structure model for mammalian 5.85S rRNA proposed by Nazar, Sitz, & Busch [J. Biol. Chem (1975) 250, 8591--8597]. Five out of six regions that are depicted in the model as single-stranded loops contain cytidine residues that are reactive towards bisulphite at 25 degrees C (the other loop contains no cytidine). The cytidine residue nearest to the 3'-terminus is also reactive. Several cytidines residues that are internally located within proposed double-helical regions show little or no reactivity towards bisulphite, but the cytidine residues of several C.G pairs at the ends of helical regions show some reactivity, and one of the proposed loops appears to contain six nucleotides, rather than the minimum of four suggested by the primary structure. Two cytidine residues that are thought to be 'looped out' by small helix imperfections also show some reactivity.     

Nucleotide sequence of Rattus norvegiens mitochondrial DNA that includes the genes for tRNAile, tRNAgln and tRNAf-met

The nucleotide sequence of a segment of mtDNA from Rattus norvegiens (rat) which contains the genes for tRNA^ile, tRNA^gl and tRNA^f-met has been determined. A detailed comparison has been made between this sequence and the corresponding sequences of mouse, human and bovine mtDNAs with regard to the primary and secondary structure of the tRNA genes, the regions connecting the tRNA genes, and the regions flanking the tRNA genes which code for the carboxyl terminus of URF-1 and the amino terminus of URF-2. No differences were found in the nucleotide sequences of the genes for tRNA^ile, tRNA^gln and tRNA^f-met in mtDNAs from three different female lines of rats (SASCO-1, SASCO-2 and Wild-UT) that differ by substitutions of 0.8% to 1.8% of their total nucleotides.     

Nucleotide sequence variants of Rattus norvegicus mitochondrial DNA

The mitochondrial DNA (mtDNA) molecules of different albino, domesticated rats (Rattus norvegicus) of the SASCO colony are of two kinds (SASCO-1 and SASCO-2) in regard to their sensitivity at certain sites to a number of restriction enzymes. MtDNA molecules from Utah wild R. norvegicus (Wild-UT) have sensitivities to restriction enzymes which differ at some sites from either SASCO-1 or SASCO-2 mtDNA molecules. Four single nucleotide differences were found among the HindIII F fragments (169 nucleotides) of SASCO-1, SASCO-2, and Wild-UT mtDNAs. Arguments are presented in favor of the interpretation that each variant nucleotide is the third nucleotide of the codon containing it, and that none of the four differences would result in a difference in the respective amino acid translated.Dedicated to Professor W. Beermann on the occasion of his 60th birthday