A novel Euglena gracilis chloroplast operon encoding four ATP synthase subunits and two ribosomal proteins contains 17 introns

Molecular identification of medicinal plants with amplicon length polymorphism using universal DNA barcodes of the atpF-atpH, trnL and trnH-psbA regions

Amplification success and species discrimination efficiency of universal DNA barcode primers (trnH-psbA, trnL, ycf1b, atpF-atpH, matK and rbcL) was evaluated in 46 representative medicinal plant species of 28 families on agarose gel. The results showed that amplicons length polymorphism revealed by the primers atpF-atpH, trnH-psbA and trnL can simultaneously discriminate all the 46 species under study precisely. Some of the plant species included in this study are used as potential adulterants to other plant species. We were able to successfully discriminate the plant species from their potential substitute. Vitex negundo is an adulterant of Ocimum sanctum which has been successfully discriminated by all these three markers. Another example of adulteration between Bacopa monnieri and Centella asiatica was successfully discriminated by atpF-atpH, trnL and trnH-psbA on the basis of variability in amplicon length of these two medicinal herbs. Further, Cassia tora and Cassia fistula are also adulterants for each other and variability in amplicon length between these two species was revealed by atpF-atpH and trnH-psbA markers. A colour code distance matrix based on amplicon length polymorphism was designed to select primers which can effectively discriminate plants species on the basis of their amplicon length. Discrimination of plant species with the universal markers on agarose gel is a noble and inexpensive approach as it does not require sequencing of amplicons. This procedure will provide a way for the development of diagnostic markers to identify adulteration not only in herbal drug formulations but also in food material.

Chloroplast ribosomes and protein synthesis

Consistent with their postulated origin from endosymbiotic cyanobacteria, chloroplasts of plants and algae have ribosomes whose component RNAs and proteins are strikingly similar to those of eubacteria. Comparison of the secondary structures of 16S rRNAs of chloroplasts and bacteria has been particularly useful in identifying highly conserved regions likely to have essential functions. Comparative analysis of ribosomal protein sequences may likewise prove valuable in determining their roles in protein synthesis. This review is concerned primarily with the RNAs and proteins that constitute the chloroplast ribosome, the genes that encode these components, and their expression. It begins with an overview of chloroplast genome structure in land plants and algae and then presents a brief comparison of chloroplast and prokaryotic protein-synthesizing systems and a more detailed analysis of chloroplast rRNAs and ribosomal proteins. A description of the synthesis and assembly of chloroplast ribosomes follows. The review concludes with discussion of whether chloroplast protein synthesis is essential for cell survival.

A group III twintron encoding a maturase-like gene excises through lariat intermediates

The 1605 bp intron 4 of the Euglena gracilis chloroplast psbC gene was characterized as a group III twintron composed of an internal 1503 nt group III intron with an open reading frame of 1374 nt (ycf13, 458 amino acids), and an external group III intron of 102 nt. Twintron excision proceeds by a sequential splicing pathway. The splicing of the internal and external group III introns occurs via lariat intermediates. Branch sites were mapped by primer extension RNA sequencing. The unpaired adenosines in domains VI of the internal and external introns are covalently linked to the 5' nucleotide of the intron via 2'-5' phosphodiester bonds. This bond is susceptible to hydrolysis by the debranching activity of the HeLa nuclear S100 fraction. The internal intron and presumptive ycf13 mRNA accumulates primarily as a linear RNA, although a lariat precursor can also be detected. The ycf13 gene encodes a maturase-like protein that may be involved in group III intron metabolism.

Gene structure and expression of a novel Euglena gracilis chloroplast operon encoding cytochrome b6 and the beta and epsilon subunits of the H(+)-ATP synthase complex

The genes encoding cytochrome b6 of the chloroplast cytochrome b6/f complex (petB) and the ATP synthase CF1-beta subunit (atpB) and epsilon-subunit (atpE) were identified on the EcoD fragment of the Euglena gracilis chloroplast genome. The complete nucleotide sequence of these three genes was determined. The petB-atpB-atpE genes are cotranscribed as a tricistronic operon. This gene organization differs from that of land plants in which atpB-atpE form a discistronic operon, and petB is within the psbB-ycf8-psbH-petB-petD operon. Euglena cytochrome b6 and the beta-subunit of the chloroplast ATP synthase are very similar in derived amino acid sequence to the corresponding gene products from other organisms. The epsilon-subunit of the chloroplast ATP synthase complex is more divergent. In Euglena, the petB-atpB-atpE genes contain introns, including two twintrons, at eight different positions. All of the intron positions were confirmed by analysis of cDNAs. Two independent intercistronic RNA processing events and 11 splicing reactions lead to the accumulation of the mature petB, atpB and atpE monocistronic mRNAs.

Group II and group III introns of twintrons: potential relationships with nuclear pre-mRNA introns

Two new and important features of introns have emerged from analysis of the Euglena gracilis chloroplast genome. One is a new class of introns, designated group III, that may be the closest contemporaries to nuclear pre-mRNA introns. The second is introns that are interrupted by other introns termed twintrons.

A complex twintron is excised as four individual introns

Twintrons are introns-within-introns excised by sequential splicing reactions. A new type of complex twintron comprised of four individual group III introns has been characterized. The external intron is interrupted by an internal intron containing two additional introns. This 434 nt complex twintron within a Euglena gracilis chloroplast ribosomal protein gene is excised by four sequential splicing reactions. Two of the splicing reactions utilize multiple 5'- and/or 3'-splice sites. These findings are evidence that introns with multiple active splice sites can be formed by the repeated insertion of introns into existing introns.