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H R Mahler

Publications and source records attributed to H R Mahler.

At least 37 records · Page 2Linked to original sources
PubMed1981

Presynaptic localization of phosphoprotein B-50.

A major phosphoprotein of synaptic membranes, the phosphorylation of which is stimulated by Ca2+ and inhibited by ACTh, appears to be identical with protein B-50 described by Zwiers, Schotman and Gispen [40]. We have investigated its subsynaptic localization by means of a variety of subfractionation techniques and compared it with that of a number of other phosphoproteins found in synaptic membranes. It appears to be predominantly, if not exclusively, associated with presynaptic membranes of low bouyant density. This localization pattern is similar to, but somewhat more extreme than that exhibited by Protein I, as a brain specific phosphoprotein studied by Greengard and his collaborators [11].

Animals↗
PubMed1981

Regulatory interactions between mitochondrial genes: interactions between two mosaic genes.

We have studied the mitochondrial DNA and the phenotypes of strains of Saccharomyces cerevisiae with specific intervening sequences in two mosaic genes: cob (the gene for apocytochrome b) and oxi3 (the gene for subunit I of cytochrome oxidase). The results suggest the following. (i) The presence of an intervening sequence downstream encompassing the intron box7 is sufficient for the regulation of oxi3 by cob (BOX phenotype); two sequences (containing intron loci box3 and box10) upstream in cob and two in oxi3 are dispensable. (ii) Strains without the two sequences upstream still contain the downstream sequence and the competence to specify a functional trans-acting element. Mutational lesions in this segment are phenotypically indistinguishable from box7 mutants, including the accumulation of polypeptides with homologous amino acid sequences. (iii) A catabolite-sensitive BOX phenotype, characteristic of mutants in the first exon, requires the simultaneous presence of an adjacent intervening sequence. A model is presented in which a hypothetical product specified by an intron (locus box7) of the cob gene controls the expression of a second mosaic gene (oxi3).

DNA Restriction Enzymes↗
PubMed1981

Calcium-stimulated adenosine triphosphatases in synaptic membranes.

We have investigated the properties of several ATPases present in synaptic membrane preparations from the cerebral cortex of rat. In addition to the intrinsic (Na+ + K+)-ATPase and a low level of contaminating Mg2+-ATPase of mitochondrial origin, both of which could be controlled by the addition of ouabain and azide, respectively, four activities were studied: (1) a Mg2+-ATPase; (2) a Mg2+-independent activity requiring Ca2+ ions at high concentrations; (3) a (Ca2+ + Mg2+)-ATPase with a high affinity for Ca2+, which were enhanced further (4) by the inclusion of calmodulin (33 nM for half-maximal activity). In the presence of 0.5 mM-EGTA in the buffer used, half saturation for these respective metal ions was observed at 0.9 mM for (1), 1.0 mM for (2), and approximately 0.3 mM for (3) and (4); the latter values correspond to concentrations of free Ca2+ of 0.38 and 0.18 microM for (3) and (4), respectively. The level of activities observed, all in nmol X min-1 X mg-1, under optimal conditions of 37 degrees C, was in a number of preparations (n in parenthesis): for (1) 446 +/- 19 (19); for (2) 362 +/- 18 (3) for (3) 87 +/- 13 (12); and for (4) 161 +/- 29 (12). The (Ca2+ + Mg2+)-ATPase, both in the presence and absence of calmodulin, could be inhibited specifically by a number of agents (approximate I0.5 in parentheses) which, at these concentrations, showed little or no potency against the other activities; among them were vanadate (less than or equal to 10 microM), La3+ (75 microM), trifluoperazine, and other phenothiazines (50 microM). These properties suggest that the (Ca2+ + Mg2+)-ATPase described may be responsible for calcium transport across one (or more) of the several membranes present in nerve endings and contained in the preparation used.

Adenosine Triphosphatases↗
PubMed1980

Mutations within an intron and its flanking sites: patterns of novel polypeptides generated by mutants in one segment of the cob-box region of yeast mitochondrial DNA.

We have undertaken a systematic examination of the polypeptides accumulating in thirteen (out of 23) mutants in the intron cluster box7 and its flanking clusters box2 and box9 of the cob-box (cytochrome b) region of the mitochondrial genome of Saccharomyces cerevisiae. We have subjected these polypeptides to fingerprint analysis, both sequential and in parallel, with two proteases in order to disclose sequence homologies and differences between the different novel polypeptides themselves, and between them and the wild type product of the gene, i.e. apocytochrome b. One of our aims has been to establish the existence of possible correlations between the nature of the novel polypeptides and the fine structure genetic map of that segment of the mitochondrial genome. Our results show that all box7 mutants accumulate the following set of polypeptides not seen in wild type cells: a) a characteristic set of "large" polypeptides consisting of three species: p56, p42 and p35 or p34.5; b) a polypeptides p23; c) a much shorter fragment (of which the apparent molecular weight varies from 12.5 to 13, according to the mutation) with the exception of two mutants; d) in addition, the majority accumulate in varying amounts a polypeptide p30 closely related to but not identical with apocytochrome b. Moreover only two box7 mutants accumulate a polypeptide in the range of mobilities corresponding to 25-27 Kd (referred to as class p26) while such a polypeptide is seen in all box9 and box2 mutants examined with one exception in box2.

Amino Acids↗
PubMed1980

Partial characterization of the plasma membrane ATPase from a rho0 petite strain of Saccharomyces cerevisiae.

Crude membrane preparations of a rho0 mutant of Saccharomyces cerevisiae exhibit Mg2+-dependent ATPase activity. Over the optimal pH range, 5.0-6.75, the apparent Vmax of the enzyme equals 590 nmoles of ATP hydrolyzed per minute per milligram protein, with an apparent Km for ATP of 1.3 mM. ATP hydrolysis is insensitive to ouabain, venturicidin, aurovertin, and the protein inhibitor described by Pullman and Monroy; inhibited by oligomycin (at high concentrations) and sodium orthovanadate, and it is sensitive to dicyclohexylcarbodiimide, p-hydroxymercuribenzoate, hydroxylamine, sodium fluoride, and sodium iodoacetate. The pH optimum and the inhibitor pattern distinguish the plasma membrane enzyme from the mitochondrial F1 ATPase still present in these cells (this activity is sensitive to efrapeptin, aurovertin, and the protein inhibitor, but resistant to DCCD). In addition, the activity of the plasma membrane enzyme and its affinity for ATP are responsive to changes in the composition of the growth medium, with the highest activity observed in cells grown on methyl-alpha-D-glucoside, a sugar which results not only in partial release from catabolite repression but also requires the induction of an active transport system for growth.

Adenosine Triphosphatases↗
PubMed1980

Mosaic organization of a mitochondrial gene: evidence from double mutants in the cytochrome b region of Saccharomyces cerevisiae.

The region coding for apocytochrome b in the mitochondrial genome of Saccharomyces cerevisiae is believed to exhibit a mosaic organization, consisting in certain strains of five exons and four introns. This model can be tested by the use of double mutants, each containing two physically, genetically and phenotypically defined mit- lesions in cis, (that is, in the same mitochondrial chromosome). Such mutants have been constructed, and the phenotypes of several examples of each of the four possible classes--exon-exon, exon-intron (downstream), intron (upstream)-exon and intron-intron--have been examined. Our results have shown that upstream mutations are always epistatic to downstream ones for polypeptide products, and that regulation of expression of cytochrome oxidase subunit I by introns is epistatic regardless of position. These findings have provided an independent verification of the mosaic model, and also suggest that at least the majority of novel polypeptides accumulating in intron mutants are hybrid products that contain sequences of the wild-type polypeptide.

Apoproteins↗
PubMed1979

Regulatory interactions between mitochondrial genes. I. Genetic and biochemical characterization of some mutant types affecting apocytochrome b and cytochrome oxidase.

The region of the mtDNA containing the structural gene for apocytochrome b is called the cob or box region. There is evidence that the same region is also involved in the regulation of cytochrome oxidase. We have isolated eight mit- mutants in this region and have ordered them using petite deletion mapping. Four of these mutants appear to map outside the boxII region on the oli2-proximal end. Analysis of restriction endonuclease fragments of the mtDNA from peptides used in the deletion mapping suggests a minimum size of 3.1 x 10(3) base pairs for the whole cob region. Although none of our mutants contained any cytochrome b or cytochrome b-linked activities, polypeptides apparently related to apocytochrome b were present in some but not all mutants. Additional regulatory effects (both positive and negative) on cytochrome oxidase by virtue of control of its subunit I were also observed. In addition to these phenotypic traits, some of the mutants accumulated novel, mitochondrially translated polypeptides not seen in wild type.

Apoproteins↗
PubMed1979

Regulatory interaction between mitochondrial genes. II. Detailed characterization of novel mutants mapping within one cluster in the cob2 region.

These studies describe the properties of three mit- mutants designated EM17, EM25, and PZ1, all mapping at two closely linked sites near one of the boundaries of the region of the mitochondrial genome concerned with the specification of cytochrome b. They all exhibit complex phenotypes affecting cytochrome b, cytochrome aa3, and additional polypeptides not found in the wild type. In the case of EM 17 this complexity can be ascribed to the presence of two mutations induced in the course of the initial mutagenic treatment: one, the cob2 mutation proper, is responsible for the loss of cytochrome b which is replaced by an altered, functionally inactive polypeptide, cytochrome b. This polypeptide can be further modified, or even eliminated, by the controlled introduction of another mutation in the cob1 segment of the cob region. The reduction in cytochrome oxidase subunit I, responsible for the effects on cytochrome aa3 and enzymatic activity in EM17, is due to a second (not mit-) mutation that has been located in the par1-proximal segment of the oxi3 region. This second mutation as well as the cob mutation can be overcome, and the respective aspect of wild type function restored to EM17, by recombination with rho- strains retaining the appropriate segment(s) of the wild type genome. The phenotype of the other two mutants is due to a single mutagenic event. This conclusion is confirmed by their ability to restore wild type functions by reversion. The mutation in EM25 appears to be due to a frameshift, which has led to premature chain termination, producing a polypeptide of Mr = 15,000 related to apocytochrome b. This change is accompanied by a decrease in the amount of subunit I of cytochrome oxidase. Revertants fall into three classes: on galactose two produce a polypeptide indistinguishable from apocytochrome b, but vary in its amount, while the third fails to increase apocytochrome b above mutant levels. Production of subunit I is increased but fails to reach wild type levels. Complete restoration of wild type functions can, however, be obtained by recombination of EM25 with rho- (cob2+) strains. Mutation PZ1 results in a complete absence of any polypeptide related to apocytochrome b and of cytochrome oxidase subunit I. These cells produce a novel polypeptide with a Mr = 45,000 not found in the wild type, and unrelated to all its normal polypeptides. Reversion or recombination with rho- (cob2+) strains results in virtually complete restoration of all wild type functions and the elimination of the novel polypeptide.

Apoproteins↗