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R A Collins

Publications and source records attributed to R A Collins.

At least 109 records · Page 6Linked to original sources
PubMed1984

Heterogeneity of vertebrate brain tubulins.

We have examined the extent of brain tubulin heterogeneity in six vertebrate species commonly used in tubulin research (rat, calf, pig, chicken, human, and lamb) using isoelectric focusing, two-dimensional electrophoresis, and peptide mapping procedures that provide higher resolution than previously available. The extent of heterogeneity is extremely similar in all of these organisms, as judged by number, range of isoelectric points, and distribution of the isotubulins. A minimum of 6 alpha and 12 beta tubulins was resolved from all sources. Even the pattern of spots on two-dimensional peptide maps is remarkably similar. These similarities suggest that the populations of tubulin in all of these brains should have similar overall physical properties. It is particularly interesting that chicken, which has only four or five beta-tubulin genes, contains approximately 12 beta tubulins. Thus, post-translational modification must generate at least some of the tubulin heterogeneity. Mammalian species, which contain 15-20 tubulin DNA sequences, do not show any more tubulin protein heterogeneity than does chicken. This suggests that expression of only a small number of the mammalian genes may be required to generate the observed tubulin heterogeneity.

Animals↗
PubMed1983

Structural variations and optional introns in the mitochondrial DNAs of Neurospora strains isolated from nature.

Mitochondrial DNAs from ten wild-type Neurospora crassa, Neurospora intermedia, and Neurospora sitophila strains collected from different geographical areas were screened for structural variations by restriction enzyme analysis. The different mtDNAs show much greater structural diversity, both within and among species, than had been apparent from previous studies of mtDNA from laboratory N. crassa strains. The mtDNAs range in size from 60 to 73 kb, and both the smallest and largest mtDNAs are found in N. crassa strains. In addition, four strains contain intramitochondrial plasmid DNAs that do not hybridize with the standard mtDNA. All of the mtDNA species have a basically similar organization. A 25-kb region that includes the rRNA genes and most tRNA genes shows very strong conservation of restriction sites in all strains. The 2.3-kb intron found in the large rRNA gene in standard N. crassa mtDNAs is present in all strains examined, including N. intermedia and N. sitophila strains. The size differences between the different mtDNAs are due to insertions or deletions that occur outside of the rRNA-tRNA region. Restriction enzyme and heteroduplex mapping suggest that four of these insertions are optional introns in the gene encoding cytochrome oxidase subunit I. Mitochondrial DNAs from different wild-type strains contain zero, one, three, or four of these introns.

Chromosome Mapping↗
PubMed1983

Comparison of biochemical and histological methods of estimating fat content of liver of dairy cows.

The degree of fatty infiltration of the liver was estimated in two herds of dairy cows using biochemical and stereological methods. Estimation of hepatic triglyceride content biochemically or of fractional volume of fat in hepatocytes stereologically are both reliable methods of assessing fatty infiltration of the liver in the dairy cow. Estimation of hepatic total lipid content is not considered an acceptable alternative because the high basal level of non-triglyceride lipid masks the increase in hepatic triglyceride content which is characteristic of fatty liver.

Animals↗
PubMed1982

Characterization of two new plasmid DNAs found in mitochondria of wild-type Neurospora intermedia strains.

Mitochondria from two Neurospora intermedia strains (P4O5-Labelle and Fiji N6-6) were found to contain plasmid DNAs in addition to the standard mitochondrial DNA species. The plasmid DNAs consist of monomeric circles (4.1-4.3 kbp and 5.2-5.3 kbp for Labelle and Fiji, respectively) and oligomers in which monomers are organized as head-to-tail repeats. DNA-DNA hybridization experiments showed that the plasmids have no substantial sequence homology to mtDNA, to each other, or to a previously characterized mitochondrial plasmid from N. crassa strain Mauriceville-lc (Collins et al. Cell 24, 443-452, 1981). The intramitochondrial location of the plasmids was established by cell fractionation and nuclease protection experiments. In sexual crosses, the plasmids showed strict maternal inheritance, the same as Neurospora mitochondrial DNA. The plasmids may represent a novel class of mitochondrial genetic elements.

Base Composition↗
PubMed1982

RNA splicing in Neurospora mitochondria. Characterization of new nuclear mutants with defects in splicing the mitochondrial large rRNA.

In Neurospora, the gene encoding the mitochondrial large (25S) ribosomal RNA contains an intervening sequence of 2.3 kb. We have identified eight nuclear mutants that are defective in splicing the mitochondrial large ribosomal RNA and that accumulate unspliced precursor RNA. These mutants identify three different nuclear genes required for the same mitochondrial RNA splicing reaction. Some of the mutants have unique phenotypic characteristics (for example, accumulation of an unusual intron RNA) that may provide insight into specific aspects of mitochondrial RNA splicing. Mutations at one locus, cyt4, are subject to partial phenotypic suppression by the electron-transport inhibitor antimycin. This phenomenon suggests that at least one component required for mitochondrial RNA splicing is regulated such that its synthesis or activity is increased in response to impairment of electron transport.

Antimycin A↗
PubMed1981

A novel extranuclear mutant of Neurospora with a temperature-sensitive defect in mitochondrial protein synthesis and mitochondrial ATPase.

[C93] is a novel, extranuclear mutant of Neurospora crassa which has a normal mitochondrial phenotype when grown at 25 degrees, but which is deficient in cytochromes b and aa3 when grown at 37 degrees (Pittenger and West 1979). In the present work, the phenotype of [C93] was characterized in greater detail. When [C93] is grown at 37 degrees, the rate of mitochondrial protein synthesis is decreased to approximately 25% that of wild type; the ratio of mitochondrial small to large ribosomal subunits is decreased to 1:4 and mitochondrial small subunits are deficient in the mitochondrially-synthesized protein, S-5. The mitochondrial ribosome assembly defects in 37 degrees-grown [C93] resemble those in chloramphenicol-treated wild-type cells and could merely be a consequence of the decreased rate of mitochondrial protein synthesis. Analysis of mitochondrial translation products by SDS gel electrophoresis suggests that 37 degrees-grown [C93] is grossly deficient in the 19,000 Mr subunit of the oligomycin-sensitive ATPase relative to other mitochondrially-synthesized proteins. The ATPase defect was not found in other extranuclear or nuclear mutants deficient in mitochondrial protein synthesis. These data and additional evidence suggest that the primary defect in [C93] may be in the assembly of the ATPase complex. The possible connection between the ATPase defect and the deficiency of mitochondrial protein synthesis is discussed.

Adenosine Triphosphatases↗
PubMed1981

Characterization of a novel plasmid DNA found in mitochondria of N. crassa.

We have identified a plasmid DNA that is found within mitochondria of wild-type N. crassa strain Mauriceville-1c (FGSC #2225), but that shows no detectable sequence homology with mitochondrial DNA. The plasmid DNA consists of an oligomeric series of circular molecules of monomer length 3.6 kb. There are two unusual clusters of restriction enzyme sites, one consisting of six Eco RI sites in a 1 kb region, and the other of five or more Pst I sites in a 0.4 kb region. RNA gel transfer hybridization experiments show a major transcript 3.3 to 3.4 kb long, close to the monomer length of the plasmid. The latter finding implies that the plasmid DNA contains specific sites for the initiation and termination of transcription.

Base Sequence↗
PubMed1980

Deletion mutants of Neurospora crassa mitochondrial DNA and their relationship to the "stop-start" growth phenotype.

"Stoppers" are a class of Neurospora crassa extranuclear mutants characterized by gross deficiencies of cytochromes b and aa3 and an unusual growth phenotype which involves irregular periods of growth andnongrowth. In the present work, mtDNAs from all four stopper mutants were found to contain deletions or insertions detectable by restriction enzyme analysis. [stp] mtDNA consists predominantly of defective molecules which retain a 16-megadalton segment (EcoRI-1, -4, and -6) of wild-type mtDNA (40 megadaltons). The other stopper mutants show smaller alterations: [stp A18t]-618, a 0.35-kilobase deletion in EcoRI-7b; [stp B2]-651, a 4-kilobase insertion in EcoRI-2; and [stp A]-574, a 5-kilobase deletion in EcoRI-2 and -10. Based on these results, we propose that "stop-start" growth results from competition between certain defective mtDNAs which have a tendency to predominate and low concentrations of less defective mtDNA species which must be retained to sustain growth. Three additional extranuclear mutants ("nonstoppers") have also been found to contain deletions in mtDNA. Remarkably, the defective mtDNA species in two of these mutants ([poky]H1-10 and [SG-3]-551) retain different sizes (18 and 13 megadlatons, respectively) of the same region retained in [stp] mtDNA (i.e., EcoRI-1, -4, and -6). The findings suggest that production of defective mtDNAs in Neurospora is nonrandom with a preferred mechanism leading to retention of this segment. It may be significant that the retained segment contains both mitochondrial rRNA genes and most mitochondrial tRNA genes. These deletion mutants may provide a tool for genetic mapping of Neurospora mtDNA.

DNA, Mitochondrial↗
PubMed1980

A correlated biochemical and stereological study of periparturient fatty liver in the dairy cow.

Liver lipids were estimated in cows eight weeks before and one and eight weeks after calving by two independent procedures. Liver lipid was estimated stereologically in Araldite-embedded sections and using thin layer chromatography and densitometry of the separated lipids. The results obtained by these methods were compared. There were significant increases in the hepatic content (g/kg liver wet weight) of total lipid, triacylglycerol and non-esterified fatty acids one week after calving, with no significant changes in the phospholipid and cholesterol content around calving. The liver lipid composition (g lipid/100 g total lipid) changed one week after calving, with an increased proprotion of triacylglycerol and a decreased proportion of phospholipids and cholesterol. There was no change in the proportion of non-esterified fatty acids. The volume fracton of the hepatocyte occupied by fat droplets increased one week after calving. There was a high correlation between the triacylglycerol content of the liver determined biochemically and the volume fraction of fat droplets lying within the hepatocyte cytoplasm determined stereologically.

Animals↗
PubMed1979

Defective splicing of mitochondrial rRNA in cytochrome-deficient nuclear mutants of Neurospora crassa.

Recent studies have shown that the gene encoding the large (25 S) mitochondrial rRNA of Neurospora crassa contains an intervening sequence of 2-2.5 kilobases that is not present in the mature 25S mitochondrial rRNA. Earlier studies had provided evidence that mitochondrial rRNAs in Neurospora are synthesized via a 32S precursor RNA that contains sequences for both the mature 19S and 25S RNA species. The present work shows that the intervening sequence is not present in 32S RNA. However, we have identified two temperature-sensitive nuclear mutants that fail to excise the intervening sequence at the nonpermissive temperature (37 degrees C). When grown at 37 degrees C, the mutants show decreased ratios of 25S to 19S RNA and accumulate a novel 35S RNA that appears to consist of 25S RNA plus most or all of the intervening sequence. The mutants are allelic but can be distinguished in temperature shift-up experiments, mitochondrial rRNA processing turning off more rapidly in one than in the other. These mutants should provide powerful new tools for studying RNA processing in eukaryotic cells.

Base Sequence↗
PubMed1979

Mitochondrial ribosome assembly in Neurospora. Two-dimensional gel electrophoretic analysis of mitochondrial ribosomal proteins.

Recent results with Neurospora crassa show that one protein (S-5, mol wt 52,000) associated with the mitochondrial (mit) small ribosomal subunit is translated within the mitochondria (Lambowitz et al. 1976. J. Mol. Biol. 107:223-253). In the present work, Neurospora mit ribosomal proteins were analyzed by two-dimensional gel electrophoresis using a modification of the gel system of Mets and Bogorad. The results show that S-5 is present in near stoichiometric concentrations in high salt (0.5 MKCl)-washed mit small subunits from wild-type strains. S-5 is among the most basic mit ribosomal proteins (pI greater than 10) and has a high affinity for RNA under the conditions of the urea-containing gel buffers. The role of S-5 in mit ribosome assembly was investigated by an indirect method, making use of chloramphenicol to specifically inhibit mit protein synthesis. Chloramphenicol was found to rapidly inhibit the assembly of mit small subunits leading to the formation of CAP-30S particles which sediment slightly behind mature small subunits (LaPolla and Lambowitz. 1977. J. Mol. 116: 189-205). Two-dimensional gel analysis shows that the more slowly sedimentaing CAP-30S particles are deficient in S-5 and in several other proteins, whereas these proteins are present in normal concentrations in mature small subunits from the same cells. Because S-5 is the only mit ribosomal protein whose synthesis is directly inhibited by chloramphenicol, the results tentatively suggest that S-5 plays a role in the assembly of mit small subunits. In addition, the results are consistent with the idea that S-5 stabilizes the binding of several other mit small subunit proteins. Two-dimensional gel electrophoresis was used to examine mit ribosomal proteins from [poky] and six additional extra-nuclear mutants with defects in the assembly of mit small subunits. The electrophoretic mobility of S-5 is not detectably altered in any of the mutants. However, [poky] mit small subunits are deficient in S-5 and also contain several other proteins in abnormally low or high concentrations. These and other results are consistent with a defect in a mit ribosomal constituent in [poky].

Chloramphenicol↗
PubMed1978

A regulatory system controlling the production of cytochrome aa3 in Neurospora crassa.

The mitochondria of the cyt-2-1, cya-3-16, cya-4-23 and 299-1 nuclear mutants and the [mi-3] and [exn-5] cytoplasmic mutants of Neurospora crassa are deficient in cytochrome aa3, while the cyb-1-1 and cyb-2-1 mutants have mitochondrial b-cytochrome deficiencies. However, the mitochondria from cyb-1-1 cyt-2-1, cyb-1-1 [mi-3] and cyb-2-1 [mi-3] double mutants contain 30% to 50% of the amount of cytochrome aa3 that is present in mitochondria from wild-type; i.e. cyb-1-1 and cyb-2-2 act as suppressors of the cytochrome aa3 deficiency phenotypes that are associated with cyt-2-1 and [mi-3] mutations. The production of cytochrome aa3 can be induced in cyt-2-1 and [mi-3] by growing cells in medium containing antimycin A, an inhibitor of electron transport in the cytochrome bc1 segment of the mitochondrial electrontransport chain. Moreover, the growth of the [mi-3] mutant is strongly stimulated by low concentrations of antimycin A. The induction of cytochrome aa3 by antimycin treatments does not occur in [exn-5], cya-4-23 and 299-1 cells; but does take place in cya-3-16 cells. Although some of the seven constituent polypeptides of cytochrome aa3 are present in mitochondria of [mi-3], the holoenzyme complex is not formed in the mutant. In contrast, the mitochondria of cyb-1-1 [mi-3] and cyb-2-2 [mi-3] double mutants contain a fully assembled cytochrome oxidase complex as well as some unassembled subunit polypeptides. The observations are indicative of the existence of at least two regulatory systems controlling the production of cytochrome aa3. One of the circuits appears to control the basal or "constitutive" production of cytochrome oxidase, the other seems to coordinate the level of cytochrome aa3 with some function of the mitochondrial cytochrome bc1 complex, possibly electron transport.

Antimycin A↗
PubMed1978

Nuclear suppressors of the [poky] cytoplasmic mutant in Neurospora crassa. III. Effects on other cytoplasmic mutants and on mitochondrial ribosome assembly in [poky].

We have previously isolated six non-allelic, nuclear mutations (sui loci) that partially suppress the growth, respiratory and cytochrome abnormalities of the extranuclear [poky] mutant. A comparison of the mitochondrial ribosome profiles of suppressed and unsuppressed [poky] strains revealed that five of the six suppressors alleviate at least partially the deficiency of mitochondrial small ribosomal subunits that is associated with the [poky] genotype. Six independently isolated Group 1 extranuclear mutants, namely [exn-1], [exn-2], [exn-4-a1, [stp-b1], [SG-1] and [SG-3-A1, which have growth and cytochrome phenotypes similar to [poky] also were found to be deficient in small subunits of mitochondrial ribosomes. Using cytochrome aa3 and b production as a criterion for mitochondrial protein synthesis, it could be shown that the nuclear su I suppressors of [poky] also suppress the other six Group I extranuclear mutants. However, differences in the efficiencies of suppression by suI suppressors suggest that at least some of Group I extrachromosomal mutants are not simply re-isolates of [poky], but represent distinct extranuclear mutations.

DNA, Mitochondrial↗