Warwick Bottomley

Comparison of chloroplast DNAs by specific fragmentation with EcoRI endonuclease

SummaryA technique has been developed whereby chloroplast DNA can be digested with EcoRI endonuclease without prior isolation of the DNA from the organelle. The specific fragmentation patterns produced show that chloroplast DNAs from different families or genera of plants have few if any bands in common, and it is not until comparisons are made between species of the same genus that similarities become apparent. The number of bands in common between species varies considerably from genus to genus and the degree of similarity of chloroplast DNAs may be correlated with how closely related the species are as judged by their ability to form viable hybrids.

Characterization of the spinach chloroplast genes for the S4 ribosomal protein, tRNAThr (UGU) and tRNASer (GGA)

SummaryThe map location and nucleotide sequence of the genes for the S4 ribosomal protein (rps4) and for tRNAThr (UGU) (trnT) and tRNASer (GGA) (trnS) on spinach chloroplast DNA have been determined. rps4 lies approximately 5 kb 3′ to atpBE in the large single copy region and is transcribed in the same direction as atpBE. It has a 178 bp leader sequence, a 603 bp coding region and 620 bp 3′ tail. The sequence of the coding region is 83% homologous with that of maize rps4 (29) and the deduced amino acid sequences from the two species are 7% homologous. The spinach and Escherichia coli S4 proteins are only 36% homologous. As in the case of maize, trnT lies upstream from and on the same strand as rps4 whereas trnS lies downstream and on the opposite strand. Transcription of rps4 apparently proceeds past trnS.

Organization and Structure of the Genes for the β and ε Subunits of Spinach and Pea Chloroplast ATPase

Chloroplast ATPase (CF1) is composed of five subunits, three of which (α,β and e) are synthesized within the chloroplast (see (1) for references) and coded by chloroplast genes (2). The γ and δ subunits are synthesized in the cytoplasm and are presumed to be coded by nuclear genes (see (1) for references). The genes for the β and e subunits map close to the gene (rbcL) for the large subunit of ribulose bisphosphate carboxylase but the gene for the α subunit is located some 40 kb away on the spinach chloroplast DNA (cpDNA) map (2). In this paper we report the results of our investigations into the structure and organization of the genes for the β and e subunits of ATPase from Spinacia oleracea and Pisum sativum chloroplasts.

Mutants as Tools for the Elucidation of Photosynthetic Processes

Genetic, biochemical and physiological analyses of photosynthetic mutants have been used for many years in attempts to broaden our understanding of the structure-function relationships of the photosynthetic apparatus. The recent development of molecular biology has given us some insight into the primary structure of plant genes and is providing the techniques for the investigation of the molecular basis of mutations which were previously only detectable through their phenotypic expression. In spite of these advances we still have little understanding of the mechanisms regulating the expression of these genes. The use of recombinant DNA techniques in directly probing and manipulating the molecular pathways responsible for particular aspects of plant performance, such as photosynthesis, may lead to significant advances in our knowledge and understanding of these processes.

Expression and Evolution of the Chloroplast ATP Synthase Genes

Although the majority of chloroplast polypeptides are imported from the cytosol, a number of them are transcribed and translated within the organelle (Ellis, 1981). Most of these chloroplast-encoded polypeptides are subunits of large complexes which contain at least one nuclear-encoded subunit, so that coordinated expression of chloroplast and nuclear genes is essential for correct biogenesis of the complexes. This is the case for the major thylakoid membrane complexes involved in photosynthesis; for example the H+-ATP synthase is composed of six chloroplast- and probably three nuclear-encoded subunits (see the preceding paper). In this paper we examine the organization, expression and evolution of the chloroplast atp genes as an initial approach to an understanding of these processes.

Structure of the Gene (tmpA) for the “32,000-Mr” Thylakoid Membrane Polypeptide of Spinacia Oleracea and Nicotiana Debneyi

One of the most rapidly labeled products of chloroplast protein synthesis is a polypeptide of Mr 32,000–36,0001,2,3,4. It is synthesized as a precursor of Mr 33,500–34,5003,4 and does not accumulate in the organelle but is rapidly turned over4. Recently the polypeptide has been shown to be involved in the binding of the herbicides atrazine and DCMU and to be part of Photosystem II with a role in electron flow5. The gene (tmpA) for this polypeptide has been mapped on the chloroplast genome of a number of plant species. In spinach, as in most other plants so far studied, tmpA is located in the large single copy region of the chloroplast genome very close to the end of one of the inverted repeat regions6.