The synthesis of chloroplast high-molecular-weight ribosomal ribonucleic acid in spinach

Isolation, characterization, phosphorylation and site of synthesis of Spinacia chloroplast ribosomal proteins

We have characterized the ribosomal proteins from Spinacia chloroplasts using two-dimensional gel electrophoresis. The 30S and 50S subunits contain 23-25 and 36 ribosomal proteins, respectively. In contrast to prokaryotic ribosomes, chloroplast ribosomes contain at least one (and possibly two) phosphorylated ribosomal proteins. Isolated chloroplasts synthesize in the presence of ((35)S) labeled methionine and cysteine at least seven 30S and thirteen 50S ribosomal proteins which are assembled into (pre)ribosomes. This suggests that about one third of the chloroplast ribosomal proteins is encoded by the chloroplast DNA itself. The identity of several labeled proteins in the two-dimensional gel electrophoretic patterns which did not comigrate with stained chloroplast ribosomal proteins is discussed.

Transcription of ribosomal DNA in chloroplasts of Spirodela oligorhizaa

The genes for the two large ribosomal RNAs (16S and 23S) and for the 4.5S rRNA in Spirodela oligorhiza chloroplast DNA are transcribed as one large, 7,000 nucleotides long precursor rRNA.Using S1-nuclease mapping, we have determined that the transcript ends 135 nucleotides 3' distal of the 4.5S rRNA gene. 5S rRNA therefore, is most likely transcribed separately.Northern blotting of chloroplast RNA with distinct probes derived from the rDNA region reveals RNAs, which can be described as intermediates in the processing of the large precursor. With these findings a pathway for the maturation of this precursor is proposed.

In Vitro Antiviral Activity of some Novel Isatin Derivatives against HCV and SARS-CoV Viruses

4-[(1,2-dihydro-2-oxo-3H-indol-3-ylidene)amino]-N(4,6-dimethyl-2-pyrimidiny)benzene sulphonamide and its derivatives were evaluated for antiviral activity against Pathogenic viruses such as Hepatitis C Virus and SARS-CoV in Vero and Huh 5-2 cells, respectively. The 5-fluoro derivative inhibited the HCV RNA synthesis at 6 mug/ml, without toxicity at a concentration up to 42 mug/ml in Huh 5-2 cells. Among the compounds tested SPIII-5F exhibits the 45% maximum protection against replication of SARS-CoV in Vero cells.

NAD turnover and utilisation of metabolites for RNA synthesis in a reaction sensing the redox state of the cytochrome b6f complex in isolated chloroplasts

NAD is normally regarded as a redox molecule or as the substrate for ADP-ribosylation reactions. In this study, we describe the rapid metabolism of NAD by Percoll-gradient-purified lettuce chloroplasts and show that the adenine moiety can be incorporated into RNA in a dark-activated reaction that senses the redox state of the cytochrome b6f complex. Isolated chloroplasts rapidly metabolised radiolabelled NAD+ to 5'-AMP (within seconds) and adenosine during a 60-min incubation in vitro; the products were analysed by high-performance liquid chromatography. No radiolabelled ADP-ribose was detected. Radioactivity was incorporated into trichloroacetic-acid-insoluble material during this period, with approximately 2-4-fold more incorporation occurring in the dark. Most of this radiolabel was rendered acid-soluble by dilute alkaline digestion at 37 degrees C, yielding an approximately equal mixture of 2'-AMP and 3'-AMP, and by RNase digestion, identifying the acid-insoluble radioactive material as RNA. Protein-bound ADP-ribose would have yielded 5'-AMP and/or oligomeric/polymeric ADP-ribose after alkali digestion. The utilisation of NAD metabolites for RNA synthesis was restricted to the thylakoid compartment of the chloroplast. The use of a variety of electron-transport inhibitors such as 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, bromanil (tetrabromo-1,4-benzoquinone), electron donors (dithiothreitol), electron acceptors (ferricyanide) and an uncoupler showed that the incorporation of radiolabel from NAD into acid-insoluble material was favoured when the cytochrome b6f complex was in the oxidised state (as pertaining to incubations in the dark).

Initiation of rrn transcription in chloroplasts of Euglena gracilis bacillaris

The site of initiation of chloroplast rRNA synthesis was determined by S1-mapping and by sequencing primary rRNA transcripts specifically labeled at their 5'-end. Transcription initiates at a single site 53 nucleotides upstream of the 5'-end of the mature 16S rRNA under all growth conditions examined. The initiation site is within a DNA sequence that is highly homologous to and probably derived from a tRNA gene-region located elsewhere in the chloroplast genome. A nearly identical sequence (102 of 103 nucleotides) is present near the replication origin. The near identity of the two sequences suggests a common mode for control of transcription of the rRNA genes and initiation of chloroplast DNA replication. The related sequence in the tRNA gene-region does not appear to serve as a transcript initiation site.

Sequence organization of the chloroplast ribosomal spacer ofSpinacia oleracea including the 3' end of the 16S rRNA and the 5' end of the 23S rRNA

The 2201-bp spacer between the chloroplast ribosomal 16S and 23S genes ofSpinacia oleracea was sequenced. It contains the genes of the tRNA(Ile) (GAU) and tRNA(Ala) (UGC) which are both interrupted by introns of respectively 728 and 816 bp. These introns belong to the class II according to the classfication of Michel and Dujon [17]. Comparison of the rDNA spacer sequence of maize, tobacco and spinach indicates that no conserved polypeptide is encoded within the introns of the two tRNA genes and that the two main insertions/deletions between the three plants are located within two loops of the class II introns secondary structure, which is therefore conserved. Based on the sequence complementarity observed between the upstream and downstream parts, of the 16S and 23S rRNA genes, RNase III-like secondary structures involved in the processing of the rRNA precursor are proposed.

Specific in vitro transcription of 16S rRNA gene by pea chloroplast RNA polymerase

A highly purified RNA polymerase preparation from pea chloroplasts has been shown to specifically transcribe the 16S rRNA gene in vitro using the recombinant pCB2-8 DNA as a template. The RNA polymerase has been found to show maximum activity and specificity with pea supercoiled rDNA as a template. At low concentrations of ribonucleoside triphosphates, the RNA polymerase selectively initiates transcription on the 16S rRNA gene. A part of the 16S rRNA gene has been sequenced. The mature 16S rRNA has been found by S1 nuclease analysis to contain sequences starting from GAAGCT. The in vitro synthesized RNA has been found to protect the same nucleotides GAAGCT. In addition, the in vitro synthesized RNA was also found to strongly protect bases starting with TATG located at about 260 bases away from the start site of the mature 16S rRNA.

Characterization of transcriptionally active DNA-protein complexes from chloroplasts and etioplasts of mustard (Sinapis alba L.)

DNA-protein complexes that are capable of RNA synthesis in vitro (transcriptionally active chromosomes) were isolated from both chloroplasts and etioplasts of mustard (Sinapis alba L.) seedlings. Analyses of the polypeptide pattern of these complexes indicate that they comprise a specific subset of plastid proteins, distinct from the overall pattern of either the soluble or membrane-bound plastic proteins. DNA-protein complexes from the two plastid types have polypeptides in common. However, at least several polypeptides are highly enriched in either the chloroplast or the etioplast DNA-protein complex. The EcoRI restriction endonuclease fragments of the DNA associated with the complexes from either plastid type are the same. They are identical with the fragments obtained from highly purified chloroplast DNA. The transcriptional activity of the chloroplast complex is more than ten times higher than the activity of the etioplast complex. However, the complexes from either plastid type are capable of transcribing DNA regions containing genes for both the plastid rRNAs and for plastid proteins. In vitro transcripts were found to hybridize not only to DNA regions for mature in vivo RNA but also to adjacent regions, indicating synthesis of precursor RNA sequences by the transcriptionally active chromosomes.

A transfer RNAArg gene of Pelargonium chloroplasts, but not a 5S RNA gene, is efficiently transcribed after injection into Xenopus oocyte nuclei

We present the primary structure of a chloroplast tRNAArgACG gene of the plant, Pelargonium zonale, and its faithful expression in Xenopus oocyte nuclei. This tRNAArg gene is located 250 bp downstream of a 5S RNA gene within a cloned 5kb long ribosomal DNA segment (Fig. 1). The Pelargonium tRNAArg gene shares 97% and 86% sequence homology with tRNAArgACG genes of Spirodela oligorhiza and Euglena gracilis chloroplasts, respectively, and also extensive homology (70%) with the corresponding gene of E. coli. It lacks an intervening sequence and, like eukaryotic tRNA genes, does not code for the 3' terminal CCA nucleotides. Moreover, the chloroplast tRNAArg gene carries all the sequence elements essential for transcription by vertebrate RNA polymerase III since it is efficiently expressed in Xenopus oocyte nuclei, even in the presence of 1 microgram/ml alpha-amanitin. In Xenopus oocyte nuclei, no transcripts of the chloroplast 5S RNA gene were detected.

The Nicotiana chloroplast genome. IX. Identification of regions active as prokaryotic promoters in Escherichia coli

The galK-expression plasmid vector system pKO1 has been used to clone Nicotiana chloroplast (ct) promoters that function in Escherichia coli. The randomly cloned promoter-containing restriction fragments have been located on the ct genome and originate both from those regions encoding ribosomal and transfer RNAs and from locations elsewhere on the ct genome. The results provide the first demonstration that sequences which function as prokaryotic promoters exist in the ct genome.

The nucleotide sequences of the regions flanking the genes coding for 23S, 16S and 4.5S ribosomal RNA on chloroplast DNA from Spirodela oligorhiza

The nucleotide sequences of the flanking regions of the genes coding for Spirodela oligorhiza chloroplast ribosomal RNA's have been determined. We have compared these sequences to the corresponding ones in chloroplast DNA of other plants and of E. coli and find a striking sequential or structural homology. The region 5'-proximal to the gene coding for 16S rRNA contains a gene coding for tRNAval, which is transcribed from the same strand. In this area three prokaryotic promoter motifs are found: one located in front of the tRNAval gene and two in the intergenic space between this gene and the 16S rRNA gene. The middle one is used for the start of the transcription of the large ribosomal RNA precursor.

Nucleotide sequence of the 16S - 23S spacer region in an rRNA gene cluster from tobacco chloroplast DNA

The nucleotide sequence of a spacer region between 16S and 23S rRNA genes from tobacco chloroplasts has been determined. The spacer region is 2080 bp long and encodes tRNAIle and tRNAAla genes which contain intervening sequences of 707 bp and 710 bp, respectively. Strong homology between the two intervening sequences is observed. These spacer tRNAs are synthesized as part of an 8.2 kb precursor molecule containing 16S and 23S rRNA sequences.

Sequencing of the 16S-23S spacer in a ribosomal RNA operon of Zea mays chloroplast DNA reveals two split tRNA genes

The nucleotide sequence of th 16S-23S spacer from a ribosomal RNA operon of Zea mays chloroplast DNA has been determined. It contains two tRNA genes, coding for tRNAlle (AUCU) and tRNAAla (GCGA), which are split by intervening sequences of 949 and 806 base pairs, respectively. Homology between the two introns suggests that they have a common origin.

The synthesis and origin of chloroplast low-molecular-weight ribosomal ribonucleic acid in spinach

Chloroplasts isolated from young spinach leaves incorporate [3H]uridine into RNA species which co-electrophorese with 5-S rRNA and tRNA, but show very little incorporation into 4.5-S rRNA. Chloroplast 4.5-S rRNA is labelled in vivo after a distinct lag period relative to 5-S rRNA and tRNA. The kinetics of labelling in vivo of chloroplast 5-S rRNA are similar to those of the immediate precursors to the 1.05 x 10(6)-Mr and 0.56 x 10(6)-Mr rRNAs, whereas the kinetics of labelling of the 4.5-S rRNAare similar to those of mature 1.05 x 10(6)-Mr and 0.56 x 10(6)-Mr rRNAs. Chloramphenicol inhibits the labelling of chloroplast 4.5-S rRNA in vivo, and concomitantly inhibits the processing of the immediate precursors to the 1.05 x 10(6)-Mr and 0.56 x 10(6)-Mr rRNAs, but has little effect on the appearance of label in chloroplast 5-S rRNA. DNA/RNA hybridization using 125I-labelled RNAs suggests that chloroplast DNA contains a 2--3-fold excess of 4.5-S and 5-S rRNA genes relative to the high-molecular-weight rRNA genes. Competition hybridization experiments show that the immediate precursor to the 1.05 x 10(6)-Mr rRNA effectively competes with 125I-labelled 4.5-S rRNA for hybridization with chloroplast DNA, and is therefore a likely candidate for a common precursor to both the 1.05 x 10(6)-Mr and 4.5-S rRNAs.