ArticlePDF Available

Targeting of a foreign protein to chloroplasts by fusion to the transit peptide from the small subunit of ribulose 1,5-bisphosphate carboxylase

Authors:

Abstract

Chimaeric genes can be constructed which fuse the transit peptide of a small subunit of the chloroplast-located ribulose 1,5-bisphosphate carboxylase with a bacterial protein. The fusion protein is translocated into chloroplasts and cleaved in a similar way to the small subunit polypeptide precursor.
© Nature Publishing Group1985
© Nature Publishing Group1985
© Nature Publishing Group1985
© Nature Publishing Group1985
© Nature Publishing Group1985
© Nature Publishing Group1985
... However, other genes have been used for fusions with great success. These include the galK (galactokinase [73]), the cat (chloramphenical transacetylase [47]), the npt (neomycin phosphotransferase [117]), and the phoA (alkaline phosphatase [57a; C. Manoil and J. R. Beckwith, Proc. Natl. ...
Article
We investigated whether the two cistrons of a dicistronic mRNA can be translated in plants to yield both gene products. The coding sequences of various reporter genes were combined in dicistronic units, and their expression was analyzed in stably transformed tobacco plants at the RNA and protein levels. The presence of an upstream cistron resulted in all cases in a drastically reduced expression of the downstream cistron. The translational efficiency of the gene located downstream in the dicistronic units was 500- to 1,500-fold lower than that in a monocistronic control; a 500-fold lower value was obtained with a dicistronic unit in which both cistrons were separated by 30 nucleotides, whereas a 1,500-fold lower value was obtained with a dicistronic unit in which the stop codon of the upstream cistron and the start codon of the downstream cistron overlapped. As a strategy to select indirectly for transformants with enhanced levels of expression of a gene which is by itself nonselectable, the gene of interest can be cloned upstream from a selectable marker in a dicistronic configuration. This strategy can be used provided that the amount of dicistronic mRNA is high. If, on the other hand, the expression of the dicistronic unit is too low, selection of the downstream cistron will primarily give clones with rearranged dicistronic units.
Article
Using a modified vector, we developed a method for DNA-mediated transformation of Chlamydomonas reinhardi with increased efficiency. The vector contained the yeast 2 microns origin of replication as a heterologous replicon. The aminoglycoside 3'-phosphotransferase (APH) gene linked to the simian virus 40 early promoter was used as an antibiotic selectable marker. The C. reinhardi transformants were resistant to 12 micrograms of G418 or 150 micrograms of kanamycin per ml. A quick-blot mRNA analysis demonstrated the presence of RNase-sensitive transcripts from the APH gene in the transformants, suggesting that the acquisition of antibiotic resistance was due to the expression of the APH gene. Southern blot analysis revealed the presence of free plasmid DNA in the transformant. The transforming vector was recovered by transforming recipient bacteria with the total DNA extracted from the C. reinhardi transformant.
Article
delta 1-Pyrroline-5-carboxylate (P5C) dehydrogenase, the second enzyme in the proline utilization (Put) pathway of Saccharomyces cerevisiae and the product of the PUT2 gene, was localized to the matrix compartment by a mitochondrial fractionation procedure. This result was confirmed by demonstrating that the enzyme had limited activity toward an externally added substrate that could not penetrate the inner mitochondrial membrane (latency). To learn more about the nature of the import of this enzyme, three gene fusions were constructed that carried 5'-regulatory sequences through codons 14, 124, or 366 of the PUT2 gene ligated to the lacZ gene of Escherichia coli. When these fusions were introduced into S. cerevisiae either on multicopy plasmids or stably integrated into the genome, proline-inducible beta-galactosidase was made. The shortest gene fusion, PUT2-lacZ14, caused the production of a high level of beta-galactosidase that was found exclusively in the cytoplasm. The PUT2-lacZ124 and PUT2-lacZ366 fusions made lower levels of beta-galactosidases that were mitochondrially localized. Mitochondrial fractionation and protease-protection experiments showed that the PUT2-lacZ124 hybrid protein was located exclusively in the matrix, while the PUT2-lacZ366 hybrid was found in the matrix as well as the inner membrane. Thus, the amino-terminal 124 amino acids of P5C dehydrogenase carries sufficient information to target and deliver beta-galactosidase to the matrix compartment. The expression of the longer hybrids had deleterious effects on cell growth; PUT2-lacZ366-containing strains failed to grow on proline as the sole source of nitrogen. In the presence of the longest hybrid beta-galactosidase, the wild-type P5C dehydrogenase was still properly localized in the matrix compartment, but its activity was reduced. The nature of the effects of these hybrid proteins on cell growth is discussed.
Article
We constructed a promoter probe vector, pGVL120, to isolate plant DNA segments with promoter activity in tobacco. Plant nuclear DNA Sau3A fragments were inserted in front of the npt-II sequence, and a mixture of recombinant plasmids was mobilized to Agrobacterium sp. and used to transform tobacco protoplasts. By kanamycin selection, transformed plant cell lines containing NPT-II T-DNAs were isolated. Eight of these cell lines were regenerated and analyzed for the levels of NPT-II activity in stem, root, midrib, and leaf. These levels demonstrated novel regulation patterns in each isolate. One cell line, T20, was analyzed in detail and found to contain four different T-DNAs. One of the recloned T-DNAs, T20-2, contains an insert of 401 base pairs in front of the NPT-II sequence, and by reintroducing this T-DNA into plant cells we could demonstrate that this insert provides a promoter sequence. The NPT-II enzyme activity under the control of the P20 promoter is especially high in stem and root, but low in leaf and callus, both in the originally isolated T20 plant and in independently isolated transformants with the T20-2 T-DNA.
Article
Full-text available
The 33-, 23-, and 16-kDa proteins of the photosynthetic oxygen-evolving complex are synthesized as precursors in the cytoplasm and transported into the thylakoid lumen of higher plant chloroplasts. In this report we have analyzed the import and maturation of these precursors, using reconstituted protein import assays and partially purified preparations of the processing peptidases involved. Precursors of the 33- and 23-kDa proteins from Spinacia and Triticum aestivum are processed by a stromal peptidase to intermediate forms; polypeptides of similar size are observed during the transport of these precursors and possibly that of the 16-kDa protein, into isolated chloroplasts. Complete maturation of the 33- and 23-kDa proteins is carried out by a thylakoidal peptidase shown previously to be involved in plastocyanin biogenesis. The data support an import mechanism involving successive cleavages by the stromal and thylakoidal processing peptidases.
Chapter
D-ribulose 1,5-bisphosphate carboxylase-oxygenase's (Rubisco) central role in photosynthesis and photorespiration makes it a likely candidate for regulation, though whether it is more or less regulated than other photosynthetic enzymes remains to be seen. Rubisco's activity in vivo certainly seems to be tightly controlled, very probably by a multiplicity of mechanisms. This chapter discusses the recent advances in the understanding of Rubisco, its mechanisms of catalysis and regulation, the synthesis and assembly of its subunits, and the role of interactions between them. The only function that the glycolate pathway seems to serve is to salvage three-quarters of the carbon diverted from photosynthesis by RuBP oxygenase as phosphoglycolate. In doing so, it consumes energy in the form of ATP and reducing equivalents. Such energy consumption may be advantageous in some circumstances. For example, it may dissipate excess photosynthetic reductant under photo-inhibitory conditions associated with CO2 limitation. Rubisco stands at the interface between the inorganic and organic phases of the biosphere's carbon cycle, catalyzing the only reaction by which atmospheric CO2 may be acquired by living organisms.
Article
Full-text available
We have used an in vitro reconstitution system, consisting of cell-free translation products and intact chloroplasts, to investigate the pathway from synthesis to assembly of two polypeptide subunits of the light-harvesting chlorophyll-protein complex. These polypeptides, designated 15 and 16, are integral components of the thylakoid membranes, but they are products of cytoplasmic protein synthesis. Double immunodiffusion experiments reveal that the two polypeptides share common antigenic determinants and therefore are structurally related. Nevertheless, they are synthesized in vitro from distinct mRNAs to yield separate precursors, p15 and p16, each of which is 4,000 to 5,000 daltons larger than its mature form. In contrast to the hydrophobic mature polypeptides, the precursors are soluble in aqueous solutions. Along with other cytoplasmically synthesized precursors, p15 and p16 are imported into purified intact chloroplasts by a post-translational mechanism. The imported precursors are processed to the mature membrane polypeptides which are recovered exclusively in the thylakoids. The newly imported polypeptides are assembled correctly in the thylakoid lipid bilayer and they bind chlorophylls. Thus, these soluble membrane polypeptide precursors must move from the cytoplasm through the two chloroplast envelope membranes, the stroma, and finally insert into the thylakoid membranes, where they assemble with chlorophyll to form the light-harvesting chlorophyll protein complex.
Article
Full-text available
We have isolated and characterized a full–length cDNA clone encoding the precursor to the small subunit of wheat ribulose–1,5–bisphosphate carboxylase. From the nucleotide sequence, we deduce that the precursor contains the mature small subunit of 128 amino acid residues and an amino–terminal transit sequence of 47 amino acid residues. Southern blot analysis reveals that the small subunit precursor is encoded by a multigene family. One member of the family has been isolated. Nucleotide sequence and R–loop analyses show that it contains only one intron which separates the coding sequence of the transit peptide from that of the mature protein. This gene is expressed in vivo, as shown by mRNA hybridization to a specific probe from its 3' non–coding region.
Chapter
Ribulose-1,5-bisphosphate (RuBP) carboxylase is the major stromal protein in chloroplasts from C3 plants. It performs the first step in the Calvin cycle and is composed of 8 large subunits and 8 small subunits. The large subunits, of 53,000 daltons, are encoded by chloroplast DNA and the small subunits, of 14,000 daltons, are encoded by nuclear DNA (1,2). The small subunit is synthesized as a 20,000 dalton precursor, on free cytoplasmic ribosomes (3–6). This precursor functions in the post-translational transport of the small subunit from the site of synthesis into chloroplasts (5,6).
Article
Recent studies have established that transport across chloroplast envelopes of proteins which are synthesized by cytoplasmic ribosomes can occur by a post-translational mechanism (1,2). Dobberstein et al. (3) first discovered that a major chloroplast stromal protein, the small subunit (S) of ribulose 1,5-bisphosphate carboxylase (RuBPCase) is synthesized by free polysomes in the green alga, Chlamydomonas reinhardtii. Moreover, they found that translation of the small subunit messenger RNA in vitro yields a precursor (pS) 4000–5000 daltons larger than the mature protein. Upon incubation with a cell-free Chlamydomonas extract pS can be processed to the mature form and a small peptide fragment designated the transit peptide (4,5). Dobberstein et al. (3) proposed that transport of the RuBPCase small subunit in vivo occurs after it is completely synthesized and that the transit sequence on pS facilitates its post-translational interaction with the chloroplast envelope. This proposed mechanism is fundamentally distinct from the co-translational transport across endoplasmic reticulum membranes of proteins which are synthesized by membrane-bound ribosomes (6,7). Precursor forms of the RuBPCase small subunit also have been found among the translation products of spinach (1), pea (1,2,8) and duckweed (9) mRNA in cell-free systems.
Chapter
Why should we be interested in chloroplast protein synthesis? There are two answers to this question. The major conceptual challenge in biology at the present time is to unravel the molecular basis of differentiation. The leaf is a highly differentiated tissue because of the presence of chloroplasts. Moreover, chloroplasts are easy to isolate, and contain massive amounts of ribulose bisphosphate carboxylase (or Fraction I protein), which catalyses the initial steps in both photosynthesis and photorespiration. The sheer abundance of this protein makes it ideal for studies on the control of protein synthesis, and it is no accident that the first reported in vitro translation of a specific messenger RNA for a plant enzyme produced the large subunit of Fraction I protein1. The second reason for being interested in chloroplast protein synthesis derives from the fact that chloroplasts represent an extranuclear genetic system. When it is realised that most, if not all, eukaryotic cells possess extranuclear genetic systems, the significance of this aspect of chloroplasts is seen to extend beyond photosynthesis and differentiation.
Article
A precursor (pS) to the small subunit (S) of ribulose1-,5-bisphosphate carboxylase is the major product of cell-free protein synthesis directed by poly(A) containing RNA from Chlamydomonas reinhardtii. We present sequence data for in vitro-synthesized pS, for in vitro-synthesized S that in generated from pS by posttranslational incubation with a Chlamydomonas cell extract, and for in vitro-synthesized, mature S. We show that pS contains an NH2-terminal extension of 44 amino acid residues that is removed by cleavage at the correct site when pS is converted to S by an endoprotease present in the Chlamydomonas cell extract.
Article
A pea nuclear gene encoding the small subunit of ribulose-1,5-bisphosphate carboxylase was inserted into the tumor-inducing (Ti) plasmid of Agrobacterium tumefaciens and transferred into petunia cells by in vitro transformation. The transferred pea rbcS gene is expressed in petunia cells under the transcriptional control of its own promoter in a light-dependent fashion similar to that observed in pea leaves. In contrast, a nonphotosynthetic chimeric gene containing a nopaline synthase promoter is expressed constitutively in both light- and dark-grown tissues. In the transformed cells, transcripts from the pea rbcS gene are processed correctly and translated to yield an authentic pea small subunit polypeptide which is localized in chloroplasts.
Article
The small subunit of the chloroplast enzyme ribulose bisphosphate carboxylase is synthesised as a precursor of higher molecular weight when poly A–mRNA from pea cytoplasmic polysomes is translated by wheat-germ ribosomes. This precursor is taken up into intact isolated chloroplasts, and cleaved to its final size in the absence of protein synthesis. It is deduced that the signal hypothesis does not apply to chloroplasts; an envelope carrier mechanism is proposed.
Article
Light stimulates the uptake of polypeptides synthesized in vitro into intact chloroplasts. The light-stimulated uptake is inhibited by uncouplers, but not by the electron transport inhibitor dichlorophenyldimethylurea (DCMU) or the protein synthesis inhibitor chloramphenicol(CAP). Addition of ATP to the uptake mixture in the dark mimics the light stimulation of transport, and it reverses the uncoupler inhibition of transport in the light. These data demonstrate that cytoplasmically synthesized polypeptides are imported into the chloroplast by an energy-dependent process.