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O Schmidt

Publications and source records attributed to O Schmidt.

At least 91 records · Page 5Linked to original sources
PubMed1983

Distribution of characteristic membrane proteins in granum and stroma thylakoids.

Membrane fractions obtained by ultrasonication of Vicia faba thylakoids were analyzed by sodium dodecyl sulphate gel electrophoresis. The polypeptide patterns revealed a six-times-higher ratio of the apoprotein (1) of P700 chlorophyll a protein to the apoprotein (2) of one of the chlorophyll a proteins in photosystem II in the light (stroma) fraction as compared with the heavy (grana) fraction indicating different distribution of the two photosystems. Additionally, the light fraction was clearly depleted in chlorophyll a/b apoproteins 2a and 2b of the light-harvesting complex and enriched in CF1 alpha and beta subunits. In contrast to the fairly constant ratio of the CF1 subunits the ratio of chlorophyll a/b apoprotein 2a/2b differed significantly between the light and heavy fraction suggesting a different composition for light-harvesting complex in stroma and grana regions of the thylakoids.

Apoproteins↗
PubMed1981

In vitro transcription of cloned 5S RNA genes of the newt Notophthalmus.

Recombinant plasmids that carried genes coding for 5S ribosomal RNA of the newt, Notophthalmus viridescens, were transcribed in vitro with extracts of Xenopus laevis oocyte nuclei. Plasmids containing multiple repeats of the 5S gene and spacer directed accurate transcription of 5S RNA (120 bases). Individual repeat units were recloned by inserting Sau 3A restriction fragments into the Bam HI site of plasmid pBR322. Because each repeat was cut by the enzyme within the coding region, the inserts had incomplete coding regions at their ends and spacer sequences in the middle. The DNA of these subclones directed synthesis of a 5S-size RNA that contained both plasmid and 5S RNA sequences. Transcription initiated in the vector, proceeded through the gene segment coding for nucleotides 41-120, and terminated at the end of the gene. The initiation of in vitro transcription required neither the original 5' flanking sequences of the spacer nor the first third of the gene. We conclude that intragenic DNA sequences control the initiation of transcription. Other subclones that include pseudogenes gave rise to some transcripts 156 nucleotides long. These long transcripts represented continuation of transcription through the 36-base-pair pseudogene that is located immediately downstream from the 5S gene. However, most transcripts of these subclones terminated at the end of the normal gene before the beginning of the pseudogene. It is probable that a run of four or more Ts serves as part of the termination signal.

Animals↗
PubMed1980

Dimeric tRNA precursors in yeast.

Two DNA fragments, each containing tRNA(Arg)3 and a tRNA(Asp) gene in close conjunction, have been isolated from different genomic regions of Saccharomyces cerevisiae. Nucleotide Nucleotide sequence analysis of the gene regions revealed that in both fragments the tRNA(Arg)3 coding region is located 5'-proximal to the tRNA(Asp) coding region. They are separated by an identical spacer of 10 nucleotides. Although the 5'-flanking sequences are different in the two plasmids, some similarities are observed. To test the mode of expression of this gene configuration, we transcribed the DNA fragments in a Xenopus oocyte nuclear extract. Specific transcription of the yeast tRNA genes took place in an RNA precursor which comprised both tRNA species. We report here that the precursor RNA was processed to the mature-sized tRNA molecules, indicating the presence of an enzyme activity in the Xenopus nucleus capable of cutting a dimeric tRNA precursor. This is the first observation of a eukaryotic dimeric tRNA precursor.

Animals↗
PubMed1980

Dimeric transfer RNA precursors in S. pombe.

Sequence analysis of a Schizosaccharomyces pombe DNA fragment revealed two tRNA coding regions separated by a seven nucleotide spacer. the 5'-proximal tRNA gene encodes a tRNAUCGSer sequence, which is interrupted by a 16 nucleotide intron at the 3' side of the base adjacent to the anticodon. The second tRNA gene encodes an initiator tRNAMet sequence. This DNA fragment, cloned into pBR322, was used as template for in vitro transcription in a nuclear extract of Xenopus oocytes. The tRNA genes were transcribed into one RNA precursor which contained both tRNA sequences. The primary transcription product initiates with pppG, contains a 9 nucleotide leader sequence, a 16 nucleotide intron, a 7 nucleotide spacer between the two tRNA molecules and an 8--9 nucleotide trailer sequence. RNA initiation was only observed upstream of the 5'-proximal tRNASer. We used RNA analysis to establish a sequence of the enzymatic steps of tRNA maturation in the nuclear extract. The first step in processing the dimeric precursor is an endonuclease cleavage which generates the mature 5' end of the tRNAMet. Further steps include the removal of the flanking sequences and addition of the CCAOH 3' terminus. The last step is the splicing of the tRNASer precursor to remove the intervening sequence.

Ascomycota↗
PubMed1980

Two control regions for eukaryotic tRNA gene transcription.

Two Drosophila tRNALys genes with identical coding sequences were shown to transcribe with very different efficiences in nuclear extracts from Xenopus oocytes. The use of recombinant plasmids in which the 5'-flanking sequences of these genes were either "switched" or replaced by defined pBR322 sequences revealed two control regions for tRNA gene transcription. An internal control region comprising the mature tRNA coding sequence (and possibly its 3'-flanking sequences) is sufficient for transcription initiation, and an external control region comprising the 5'-flanking sequences represses this transcription. All transcripts have short leader sequences. Altered precursor tRNAs transcribed from truncated tRNALys genes (missing a single base pair in the acceptor stem) are not processed well in vitro.

Animals↗
PubMed1979

The nucleotide sequence of a cloned Drosophila arginine tRNA gene and its in vitro transcription in Xenopus germinal vesicle extracts.

The DNA sequence of a cloned gene specifying Drosophila tRNA2Arg has been determined. Transcription of this gene in extracts from Xenopus germinal vesicles yielded a precursor RNA containing a seven-nucleotide leader sequence at the 5' side of the mature tRNA with pppGp as the 5'-terminal nucleotide. Transcription continues for at least eight nucleotides past the 3' terminus of the coding region of the gene and terminates over a stretch of seven T residues. The isolation of the primary transcript was facilitated by incorporation of 5'-(gamma-S)GTP into the 5' terminus of the precursor RNA and by its retention on mercury-agarose. The Drosophila tRNAArg gene does not contain an intervening sequence nor the C-C-A sequence corresponding to the 3' terminus of the mature tRNA. The nucleotide sequence of Drosophila tRNAArg formed in the in vitro system differs only in four positions from that of mouse tRNAArg.

Animals↗
PubMed1979

In vitro transcription and processing of a yeast tRNA gene containing an intervening sequence.

A gene for Saccharomyces cerevisiae tRNATrp has been sequenced which contains an intervening sequence of 34 bp (H. S. Kang and J. Abelson, unpublished results). The mutant yeast strain ts-136 accumulates a precursor to tRNATrp which contains mature ends and is colinear with the tRNATrp gene. A nuclear extract from Xenopus oocytes is capable of supporting transcription of the tRNATrp gene contained on plasmid pBR313. The products are precursor tRNAs which contain the intervening RNA sequence. The Xenopus extract accurately splices the precursor transcript to mature-sized tRNATrp.

Animals↗
PubMed1978

Specific transcription of eukaryotic tRNA genes in Xenopus germinal vesicle extracts.

Cloned tRNA genes from Drosophila and from yeast have been transcribed faithfully in extracts prepared from Xenopus germinal vesicles. The newly formed RNA is composed of precursor tRNAs (of 5S RNA size) and of tRNAs. The plasmid pCIT12 carries genes for Drosophila tRNALys, tRNAArg, and tRNAAsn, Nucleotide analysis of one RNA species transcribed from pCIT12 DNA showed it to be identical to Drosophila tRNALys; it even contained some of the modified nucleotides expected for this tRNA. This RNA species is formed in the germinal vesicle extract via a larger precursor tRNA molecule that does not contain nucleotide modifications. This simple transcription system should aid studies aimed at defining the regulatory DNA regions responsible for eukaryotic gene transcription. In addition, it may provide tRNA precursors that are needed for detailed investigations of eukaryotic tRNA biosynthesis.

Animals↗
PubMed1976

The action of proteolytic enzymes on chloroplast thylakoid membranes.

Envelope- and stroma-free thylakoid membranes of Vicia faba chloroplasts were incubated with trypsin or pronase for several hours. The indigestible residue was analysed by polyacrylamide gel electrophoresis. Trypsinization resulted in a complete digestion of all proteins with the exception of the pigment-protein complexes as well as a polypeptide not yet characterized. Yet, as compared with untreated material, Complex II was found to have higher electrophoretic mobility. Electron-microscopic studies illustrate that the indigestible residue still has a preserved membrane structure. Disintegration of the thylakoid membranes by sodium dodecyl sulfate followed by trypsinization also resulted in the two complexes while all the other proteins were found to be digested. However, after removal of the lipids the protein moieties of the complexes proved to be easily digestible. From these results it is concluded that pigment-protein interaction may be an important factor in maintaining a conformation rather resistant to perturbants and proteases. In contrast to trypsin, pronase completely digested the polypeptides of the thylakoid membranes including the protein moieties of the pigment-protein complexes leaving an amorphous lipid mass. The results support the assumption that the complexes are necessary to maintain the membrane structure.

Chloroplasts↗
PubMed1975

A study of weight transmission through the knee joint with applied varus and valgus loads.

An electromechanical device is described which permits measurement of the amount of weight borne on each compartment of the knee during varying amounts of lateral angulation. A lateral angulation of only 3 degrees in either direction completely unloaded the opposite condyle. The correction to be obtained by tibial osteotomy of varus or valgus knee deformity should permit the mechanical axis of the extremity to pass the tibial spines on the side opposite the deformity. An angular deviation of 3 degrees more than that required to restore the mechanical axis to normal position is sufficient.

Adult↗