Induction of euglena transfer RNA's by light

A Cytoplasmic Regulatory Mutant of Euglena: Constitutivity for the Light-Inducible Chloroplast Transfer RNAs

An ultraviolet-induced cytoplasmic mutant (G(1)BU) of Euglena gracilis Klebs var. bacillaris Pringsheim is described. G(1)BU, in addition to being golden in color and containing smaller amounts of chlorophyll than wild type when grown in the light, is a regulatory constitutive mutant for the light-inducible chloroplast isoleucine and methionine tRNAs; i.e., these two tRNAs are present in dark-grown G(1)BU cells at approximately the levels present in light-grown wild-type cells. Six other mutants were also examined for normal control of plastid tRNA biosynthesis; all four of the aplastidic mutants (lacking appreciable plastid structures and detectable plastid DNA) are incapable of chloroplast tRNA biosynthesis, whereas two other color mutants that do contain plastids and chloroplast DNA have normal plastid tRNA regulation.

Transcriptional origin of Euglena chloroplast tRNAs

tRNA.DNA hybridization studies indicate that Euglena chloroplast tRNAs are transcriptional products of the chloroplast genome, which contains approximately 26 tRNA cistrons. Hybridization with purified chloroplast tRNA(Phe) and tRNA(Asp) shows that the chloroplast genome contains one cistron for each of these two species. No hybridization of chloroplast tRNA with nuclear DNA was observed. tRNAs from Euglena cytoplasm, Escherichia coli, and Agmenellum quadraduplicatum do not compete with chloroplast tRNA for hybridization with chloroplast DNA. Evidence is presented that photoinduction of chloroplast tRNAs is at the level of transcription rather than maturation of tRNA precursor molecules.

Light Regulation of delta-Aminolevulinic Acid Biosynthetic Enzymes and tRNA in Euglena gracilis

Chlorophyll synthesis in Euglena, as in higher plants, occurs only in the light. The key chlorophyll precursor, delta-aminolevulinic acid (ALA), is formed in Euglena, as in plants, from glutamate in a reaction sequence catalyzed by three enzymes and requiring tRNA(Glu). ALA formation from glutamate occurs in extracts of light-grown Euglena cells, but activity is very low in dark-grown cell extracts. Cells grown in either red (650-700 nanometers) or blue (400-480 nanometers) light yielded in vitro activity, but neither red nor blue light alone induced activity as high as that induced by white light or red and blue light together, at equal total fluence rates. Levels of the individual enzymes and the required tRNA were measured in cell extracts of light- and dark-grown cells. tRNA capable of being charged with glutamate was approximately equally abundant in extracts of light- and dark-grown cells. tRNA capable of supporting ALA synthesis was approximately three times more abundant in extracts of light-grown cells than in dark-grown cell extracts. Total glutamyl-tRNA synthetase activity was nearly twice as high in extracts of light-grown cells as in dark-grown cell extracts. However, extracts of both light- and dark-grown cells were able to charge tRNA(Glu) isolated from light-grown cells to form glutamyl-tRNA that could function as substrate for ALA synthesis. Glutamyl-tRNA reductase, which catalyzes pyridine nucleotide-dependent reduction of glutamyl-tRNA to glutamate-1-semialdehyde (GSA), was approximately fourfold greater in extracts of light-grown cells than in dark-grown cell extracts. GSA aminotransferase activity was detectable only in extracts of light-grown cells. These results indicate that both the tRNA and enzymes required for ALA synthesis from glutamate are regulated by light in Euglena. The results further suggest that ALA formation from glutamate in dark-grown Euglena cells may be limited by the absence of GSA aminotransferase activity.

Changes in the content of modified nucleotides of total transfer RNA of wheat seedlings during greening

The contents in minor nucleotides of total transfer RNA (tRNA) of etiolated and light-grown wheat (Triticum aestivum L.) seedlings and of seedlings illuminated for 24 or 48 h were examined. The total tRNA of seedlings illuminated 24 h contained more, and that from seedlings illuminated 48 h still more modified nucleotides than that from etiolated ones. Thus, the appearance of the characteristic minor nucleotides of tRNA of light-grown wheat seedlings needs a rather long greening period, of at least 48 h.

Subcellular localization of cytokinins in transfer ribonucleic Acid

Evidence on the localization of cytokinins in chloroplast tRNA was obtained by comparison of Euglena gracilis var. bacillaris light-grown and dark-grown wild type cultures and chloroplast-bleached mutant strains. The several cytokinins characteristic of tRNA were separated by Sephadex LH-20 column chromatography of the hydrolysates and were quantitatively determined by tobacco bioassays of the eluates. The results indicate that 6-(3-methyl-2-butenylamino)-9-beta-d-ribofuranosylpurine (i(6) A) is formed in both the cytoplasmic and chloroplast tRNA, whereas 6-(4-hydroxy-3-methyl-cis-2-butenylamino)-9-beta-d- ribofurano-sylpurine (c-io(6)A) is produced mainly in the cytoplasmic tRNA and 6-(4-hydroxy-3-methyl-2-butenylamino)-2-methylthio-9-beta-d- ribofurano-sylpurine (ms(2)io(6)A) is localized exclusively in chloroplast tRNA. The restriction of the methiolation reaction to the chloroplast is supported by results of radioisotope experiments showing that (35)S-labeled MgSO(4) is incorporated into ms(2)io(6)A in the wild type cultures, but not in the chloroplast-bleached mutant strains.

Hybridization of maize chloroplast DNA with transfer ribonucleic acids

Hybridization of [125I] tRNA to chloroplast DNA indicates that 0.60-0.75% of maize chloroplast DNA contains sequences complementary to maize tRNA, corresponding to 20-26 tRNA cistrons. Green maize seedlings contain about twice the amount of chloroplast DNA-hybridizable tRNA as etiolated maize seedings. tRNA from green or etiolated maize seedlings was also aminoacylated in vitro with 21 labeled amino acids and then incubated with filters containing chloroplast DNA, tRNAs charging a total of at least 16 different amino acids hybridized with chloroplast DNA. Most of these plastid aminoacyl-tRNAs were present in higher concentrations in tRNA isolated from green maize seedlings, although there were several exceptions. The results are consistent with the hypothesis that a complete or nearly complete set or tRNAs can be transcribed from chloroplast DNA.

Comments on the translational and transcriptional origin of Euglena chloroplastic aminoacyl-tRNA synthetases

A response to: "A consideration of Euglena gracilis W3BUL as a cytoplasmic control for the wild-type phenylalanyl-tRNA synthetase system" and "A reinvestigation of the sites of transcription and translation of Euglena chloroplastic phenylalanyl-tRNA synthetase" by J. L. Lesiewicz and D. S. Herson.

Temperature-sensitive breakdown in vivo of polysomes with mutants of Chlamydomonas reinhardii

Two temperature-sensitive mutants of Chlamydomonas reinhardii Dangeard which are defective in protein synthesis were examined. Both show breakdown of their polysomes at the restrictive temperature into monosomes which do not contain fragments of mRNA. Many of the ribosomes still contain nascent peptides able to react with puromycin. The polysome breakdown involves only cytoplasmic (80S) ribosomes and is prevented or reversed when ribosome translocation is inhibited with cyloheximide.

Chloroplast DNA codes for transfer RNA

Transfer RNA's were isolated from Euglena gracilis. Chloroplast cistrons for tRNA were quantitated by hybridizing tRNA to ct DNA. Species of tRNA hybridizing to ct DNA were partially purified by hybridization-chromatography. The tRNA's hybridizing to ct DNA and nuclear DNA appear to be different. Total cellular tRNA was hybridized to ct DNA to an equivalent of approximately 25 cistrons. The total cellular tRNA was also separated into 2 fractions by chromatography on dihydroxyboryl substituted amino ethyl cellulose. Fraction I hybridized to both nuclear and ct DNA. Hybridizations to ct DNA indicated approximately 18 cistrons. Fraction II-tRNA hybridized only to ct DNA, saturating at a level of approximately 7 cistrons. The tRNA from isolated chloroplasts hybridized to both chloroplast and nuclear DNA. The level of hybridization to ct DNA indicated approximately 18 cistrons. Fraction II-type tRNA could not be detected in the isolated chloroplasts.

Comparative base compositions of chloroplast and cytoplasmic tRNAPhe's from Euglena gracilis

The nucleoside compositions of chloroplast and cytoplasmic tRNAPhe's from Euglena gracilis have been determined. The modified nucleoside compositions of these two tRNAs indicate that tRNAPheChl is more similar to procaryotic (E. coli) tRNAPhe than to either the Euglena cytoplasmic tRNAPhe or other eucaryotic cytoplasmic tRNAPhe's.

A consideration of Euglena gracilis W3BUL as a cytoplasmic control for the wild-type phenylalanyl-tRNA synthetase system

The studies described indicate that the UV bleached mutant, Euglena gracilis W3BUL does not serve as a suitable cytoplasmic control for the phenylalanyl-tRNA synthetase system. Chromatography of wild-type E. gracilis on Sephadex G100 revealed three peaks of activity identified as the chloroplastic, cytoplasmic and mitochondrial enzymes. The chloroplastic activity was greater in log than in stationary phase cells and was the only activity recovered from purified chloroplasts. Cell-free extracts of the achloroplstic mutant, E. gracilis W3BUL, contained wild-type levels of the cytoplasmic and mitochondrial phenylalanyl-tRNA synthetases. However, no chloroplastic synthetase was detected in the mutant extracts. Anomalies in the aminoacylation behavior of the W3BUL system were observed which suggest the possibility of a mutation affecting non-chloroplastic tRNAs in this UV-induced mutant. These anomalies significantly reduce the ability of the E. gracilis W3BUL mutant to serve as a cytoplasmic control in the phenylalanyl-tRNA synthetase system.

Isoaccepting Transfer Ribonucleic Acids during Chilling Stress in Soybean Seedling Hypocotyls

Total aminoacylation of glycine and leucine transfer RNAs was compared between chilled and nonchilled hypocotyls of 7-day-old soybean seedlings. Total charging was greater for both specific transfer RNAs from nonchilled sources. Isoaccepting transfer RNA species for glycine and leucine were fractionated using reverse phase column chromatography. Leucyltransfer RNAs were fractionated into six distinct fractions with relatively small shifts appearing in specific fractions between chilled and nonchilled sources. Glycyl-transfer RNAs were fractionated into two distinct fractions with major shifts appearing for both fractions between chilled and nonchilled sources.

The sites of transcription and translation for Euglena chloroplastic aminoacyl-tRNA synthetases

We find that cycloheximide completely blocks the light-induced apearance of Euglena chloroplastic aminoacyl-tRNA synthetases in dark-grown cells of Euglena gracilis var. bacillaris. Streptomycin, on the other hand, has no effect on the light-induction of these organellar enzymes. These observations, together with the finding that an aplastidic mutant (strain W(3)BUL, which has neither significant plastid structure nor detectable chloroplast DNA) contains low levels of the chloroplastic synthetases, indicate that the chloroplastic synthetases are transcriptional products of nuclear genes and are translated on cytoplasmic ribosomes prior to compartmentalization within the chloroplasts.

Leucyl-transfer ribonucleic acid synthetase in senescing tobacco leaves

1. The activity of leucyl-tRNA synthetase obtained from tobacco leaves declined by 50% over a period of 4 days senescence induced by detachment. In addition tRNA(Leu) from senescing leaves was charged to a lesser extent than tRNA(Leu) extracted from mature leaves immediately after detachment. 2. tRNA(Leu) was charged with a synthetase preparation from either mature or senescent leaves and chromatographed on an RPC 3 column. The elution profile showed that the marked decline in specific activity of leucyl-tRNA synthetase in senescent leaves was not associated with a loss of acylation of any isoacceptor of tRNA(Leu).

Large Scale Isolation and Purification of Eyespot Granules from Euglena gracilis var. bacillaris

Large volumes of eyespot granules were isolated from homogenates of Euglena gracilis Klebs var. bacillaris Pringsheim by flotation centrifugation in a Beckman Ti-15 zonal rotor, and were further purified by centrifugation in a swinging bucket rotor. Examination with the electron microscope showed the eyespot granules to be free from other cellular material. Freezing had no apparent effect on the structure or on the absorption properties of the eyespots. Absorption spectra of pure fractions of eyespot granules free of chloroplast contamination showed the previously reported curves in the range of 360 to 520 nanometers, as well as a peak at 660 to 675 nanometers. The procedure for the large scale isolation of eyespot granules from Euglena gracilis is compared with other methods which have employed conventional centrifugation, and the significance of the use of zonal rotors for isolating large quantities of pure eyespot granules is discussed.

Ribonucleic acid from aerobically and anaerobically grown Rhodopseudomonas spheroides: comparison by hybridization to chromosomal and satellite deoxyribonucleic acid

Ribonucleic acid (RNA) species from aerobically and anaerobically grown Rhodopseudomonas spheroides were compared via hybridization to deoxyribonucleic acid (DNA). Both long-labeled and stable RNA bound to chromosomal DNA to the same extent, regardless of derivation. About 4% of the chromosomal DNA hybridized with total cell RNA and about 0.08% with stable RNA. About 4% of the mixed satellite DNA could be hybridized to total cell RNA from aerobic or anaerobic cultures, whereas essentially no stable RNA formed a hybrid with this DNA. Hybridization competition experiments with aerobic and anaerobic pulse-labeled RNA and chromosomal or satellite DNA demonstrated that no qualitative differences existed between the RNA species. It is concluded that identical species of RNA in the same relative amounts are synthesized by R. spheroides during aerobic or anaerobic growth on the same medium.

On the similarity between the tRNAs of organelles and prokaryotes

Fluorescence studies with organelle transfer RNAs separated from their cytoplasmic counterparts revealed that phenylalanine tRNA from Euglena chloroplasts or Neurospora mitochondria does not contain a fluorescent "base Y." In contrast, cytoplasmic phenylalanine tRNA from Euglena and cytoplasmic tRNA from Neurospora were found to contain fluorescent bases. The fluorescence-emission spectra of Neurospora cytoplasmic tRNAs and those of the related ascomycete Saccharomyces cerevisiue were observed to be quite different. The results support the generalization that eukaryotic tRNAs contain a fluorescent base, but indicate that their respective organelle tRNAs do not. They also indicate a striking parallelism between organelle and prokaryotic tRNAs.

Identification and origin of some chloroplast aminoacyl-tRNA synthetases and tRNAs

Light-grown, wild type Euglena gracilis contains two aminoacyl-tRNA synthetases for both phenylalanine and isoleucine. Only one of the two synthetases for each amino acid is found in isolated chloroplasts, as are the light-induced phenylalanine and isoleucine tRNAs. In each case the light-induced chloroplast tRNAs can only be acylated by the chloroplast synthetases. The chloroplast isoleucyl-tRNA synthetase is light-inducible and cannot be detected in dark-grown cells or in cells of the bleached mutant W(3)BUL. The presence of the chloroplast phenylalanyl-tRNA synthetase in W(3)BUL, which contains no chloroplast DNA or structure, indicates that this chloroplast enzyme is synthesized in the cytoplasm and is coded by nuclear genes.