Molecular cloning and sequencing of cDNA encoding the precursor to the small subunit of chloroplast ribulose-1,5-bisphosphate carboxylase

Expression of the gene coding for the small subunit of ribulosebisphosphate carboxylase during differentiation of tobacco plant protoplasts

A hybridization probe was used to study the regulation of expression of the gene coding for the small subunit of ribulose 1,5-bisphosphate carboxylase, during functional differentiation of protoplasts. A library of cDNA from poly(A)-containing RNA extracted from specially treated tobacco leaves was constructed in the plasmid pBR322 by blunt-end ligation. This library was screened by colony hybridization with 32P-labelled cDNA prepared from mRNA coding for the precursor of the small subunit. A positive colony was identified containing recombinant plasmids with a nucleotide sequence homologous to this mRNA. These plasmids, bound to diazobenzyloxymethylated cellulose paper, were then used as a hybridization probe. The results showed unambiguously that the small subunit was not transcribed in protoplasts but was transcribed in undifferentiated white and chlorophyll-containing green callus cultures derived from protoplasts. The discrepancy between these results and those obtained with classical techniques is discussed.

Purification of total cellular DNA from a single plant

A procedure is outlined for purifying DNA from a single plant. A crude organelle pellet consisting of nuclei, chromatin, chloroplasts, and mitochondria is prepared, suspended, and immediately lysed with detergents. The DNA is separated from RNA, protein, and polysaccharides by banding it in CsCl density equilibrium gradients. Ethidium bromide is included in all buffers to act as an inhibitor of DNAase activity. The DNA prepared in this manner can be digested with restriction endonucleases, separated by gel electrophoresis, and used to identify specific genes by hybridization of cloned DNA sequences.

Transport of newly synthesized proteins into mitochondria - a review

This review examines the mechanism of translocation of cytoplasmically synthesized proteins into mitochondria. Approximately 10% of the mitochondrial proteins are synthesized within the organelles while most mitochondrial proteins are coded for by nuclear genes and synthesized on cytoplasmic ribosomes. Those mitochondrial proteins synthesized on cytoplasmic ribosomes have to be transferred at some point into one of the mitochondrial compartments, a process which would require their insertion through one or both mitochondrial membranes. Data accumulated during the past five years indicate that the cytoplasmically synthesized mitochondrial proteins are synthesized on free polysomes then released into the cytoplasm. Most of the proteins examined so far are synthesized in the cytoplasm as larger precursors whose conformations may differ from the conformations of their respective mature forms. These precursor proteins become translocated into mitochondrial post-translationally and processed to their mature forms either during or immediately following translocation into the organelles. The translocation step appears to require mitochondrial ATP. Some processing activities have been localized in the matrix fractions of mitochondria from liver and yeast and they appear to be associated with soluble endopeptidases which act selectively on precursors of mitochondrial proteins. Although it is not clear how the precursor proteins interact with or recognize mitochondrial membranes, studies in yeast indicate that the interactions occur at specific regions on the other mitochondrial membranes.

Expression in E. coli of maize and wheat chloroplast genes for large subunit of ribulose bisphosphate carboxylase

Synthesis of the large subunit polypeptide of ribulose bisphosphate carboxylase can be detected in Escherichia coli cells containing the chloroplast genes from maize and wheat. The chloroplast DNA sequences contain a 'promoter' that, in Escherichia coli, initiates transcription and translation of the genes. This synthesis of large subunits has been substantially increased using the powerful lambda promoter, PL, to drive transcription of the maize gene.

Photochrome-mediated regulation of messenger RNAs for the small subunit of ribulose 1, 5-bisphosphate carboxylase and the light-harvesting chlorophyll a/b-protein in Lemna gibba

Brief red illumination (10 min/8 hr) of Lemna gibba L. G-3 growing heterotrophically in the dark increases the growth of the plants and results in a substantial increase in the levels of mRNA for two major chloroplast polypeptides. These two nuclear-coded polypeptides are the light-harvesting chlorophyll a/b-protein, an intrinsic thylakoid membrane protein, and the small subunit of the stromal enzyme ribulose 1, 5-bisphosphate carboxylase [RuP2; 3-phospho-D-glycerate carboxylyase (dimerizing), E.C.4.1.1.39]. The effect of 10 min red illumination on the dark growth of the plants is reversed by immediate far-red illumination, but the effect on the mRNA levels is not. However, this latter response can be reversed by far-red light if the time between the beginnings of the red and far-red illumination is reduced to one minute. Thus phytochrome is the photoreceptor mediating both responses, and the effect on amounts of the translatable mRNAs has a remarkably short escape time.As expected from the high level of its mRNA in the plants grown in the dark with intermittent red illumination, the small subunit of ribulose 1, 5-bisphosphate carboxylase is synthesized in these plants and accumulates without further illumination. However, despite the relatively high levels of mRNA for the chl a/b-protein in the dark grown plants, this protein does not appear to be synthesized and inserted into the thylakoid membranes until the plants are transfered into white light. Thus, the normal synthesis of this protein must require light for some post-transcriptional process.