Major mRNA species from spinach chloroplasts do not contain poly(A)

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).

Intracellular coding sites of polypeptides associated with photosynthetic oxygen evolution of photosystem II

Three hydrophilic polypeptides of approximately 34, 23, and 16 kd located on the inner thylakoid surface are associated with the water-splitting activity of photosystem II. Stable transcripts for the three proteins were found only in cytosolic (polyadenylated) RNA, suggesting that they are encoded in nuclear genes. The immunologically reacting products synthesized in a rabbit reticulocyte cell-free translation system are larger in size than the authentic mature proteins by about 6-10 kd. These larger precursors are imported post-translationally into isolated, intact chloroplasts, and are processed to their mature forms during or after translocation. The imported proteins can be extracted from thylakoids by procedures used to isolate the three native proteins of the water-splitting complex, suggesting that they have assembled properly into their final destination, the inner thylakoid surface.

Regulation of photosynthesis by reversible phosphorylation of the light-harvesting chlorophyll a/b protein

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Suitable conditions for characterization, identification, and isolation of the mRNA of the small subunit of ribulose-1,5-bisphosphate carboxylase from Nicotiana sylvestris

The products synthesized in vitro by messenger RNA (mRNA) extracted from Nicotiana sylvestris were analyzed by electrophoresis on polyacrylamide slab gels. Only three of the major polypeptides synthesized are considered here: P55, P32, and P20. P55 and P32 were translated from chloroplast mRNA. P55 corresponds to the large subunit of ribulose-1,5-bisphosphate (RuP2) carboxylase; P32 is probably a chloroplast membrane protein. P20, the polypeptide synthesized from cytoplasmic poly(A)(+) RNA, is the precursor of the small subunit of RuP2 carboxylase. The balance between P20 and P32, in which their relative proportions varied inversely, was regulated by the age of the leaves and the time of illumination; we took advantage of this phenomenon to isolate the mRNA from the small subunit in relatively large amounts. This mRNA has a molecular weight of 350,000.

Analysis of the genetic complexity and abundance classes of messenger RNA in human liver and leukemic cells

In an effort to determine the number of genes expressed as messenger RNA in disparate human tissues we have analyzed the genetic complexity of the polyribosome-associated poly(A)-containing RNA population obtained from liver and lymphoblastic leukemic cells. This was accomplished by measuring the kinetics of hybridization of mRNA to a complementary DNA probe synthesized by avian myeloblastosis virus reverse transcriptase in vitro. The results obtained from such an analysis revealed the presence of two major abundance classes of mRNA with a total genetic complexity of approximately 10,000 diverse mRNA species in both of these cell types. Diversity of mRNA species in these unrelated human cells was studied by heterologous hybridization reactions between the cDNA of one cell type and a vast excess of poly(A)-containing mRNA from another. These types of studies indicated that extensive homology (more than 80%) exists in the mRNA sequences of disparate human cell types and suggest that the vast majority of genetic information expressed as mRNA is required for the maintenance of cellular functions common to functionally different human tissues.

Messenger RNA of the large subunit of ribulose-1,5-bisphosphate carboxylase from Chlamydomonas reinhardi. Isolation and properties

Polysomes specifically synthesizing the large subunit of ribulose-1,5-bisphosphate carboxylase were isolated from Chlamydomonas reinhardi cells by the indirect immunoprecipitation method. Electrophoretic analysis showed that the immunoprecipitated polysomes were of chloroplast origin. The mRNA coding for the large subunit which was purified from immunoprecipitated polysomes migrated at the 19-S position on sucrose density gradients, and its molecular weight was estimated to be 7.3 x 10(5) by acid-urea/agarose gel electrophoresis. The mRNA was translated in vivo with a cell-free protein-synthesizing system derived from Escherichia coli to give full-length large-subunit polypeptides.

Poly(adenylic acid)-containing RNA from plastids of maize

Hybridization experiments with chloroplast DNA and 125I-labeled RNA from maize seedlings suggest that chloroplasts and etioplasts contain detectable amounts of RNA that contains poly(adenylic aicd) (poly (A)) and was transcribed from chloroplast DNA. About 6% of the total poly(A)-containing RNA isolated from maize seedlings hybridized to chloroplast DNA. Poly(A)-containing RNA could also be isolated directly from purified chloroplasts that were treated with ribonucleases to reduce cytoplasmic contamination. At least 65% of this poly(A)-containing RNA hybridized to chloroplast DNA. Chloroplast poly(A) tracts average about 45 nucleotides in length, one-half the average size of poly(A) tracts from whole cells. The poly (A) tracts themselves are probably added to plastid RNAs following their transcription, because maize chloroplast DNA was found not to contain poly(dT).

Preformed poly(A)-containing RNA in zoospores of Blastocladiella emersonii

Discharged zoospores of Blastocladiella emersonii contain poly(A)-containing RNA, which is performed during the initial stages of zoospore differentiation in the sporangium and is stable in vivo for at least 4 h. The average molecular weight of this RNA fraction is estimation to be 5.5-10(5) or 1600 nucleotides. The average length of the poly(A) sequence is approx. 100 nucleotides Poly(A)-containing RNA does not appear to accumulate in a gamma-particle fraction previously suggested to be involved in the storage of mRNA.

Large subunit ribulosebisphosphate carboxylase messenger RNA from Euglena chloroplasts

RNA from wild-type Euglena, aplastidic mutant cells, and purified chloroplasts was chromatographed on oligo(dT)-cellulose at 4 degrees. The poly(A)-containing and poly(A)-lacking fractions from each were then tested in a cell-free protein-synthesizing system from wheat germ for their abilities to specifically stimulate synthesis of large subunit ribulosebisphosphate carboxylase [EC 4.1.1.39; 3-phospho-D-glycerate carboxy-lyase (dimerizing)]. The large subunit polypeptide (59,000 molecular weight) was identified in the in vitro reaction by two-dimensional electrophoresis involving isoelectric focusing and size filtration on polyacrylamide gels. Template activity for the large subunit was detected in wild-type cells but not in aplastidic mutant strains; it was highly enriched in the isolated chloroplasts. This messenger was present only in the poly(A)-lacking RNA fraction, where it constituted the most prominent template species of chloroplast RNA. The large subunit message was freed of considerable non-messenger RNA contamination and localized to the 10-20S fraction by sucrose gradient centrifugation.