Evidence for a novel DNA component in chloroplasts of Euglena gracilis

Physical mapping of the ribosomal DNA region of Euglena gracilis chloroplast DNA

1. The relative positions of endo R . EcoRI and endo R . Bg/II cleavage sites are mapped within the linked DNA fragments Bam-E-E-D of the Euglena gracilis chloroplast DNA. 2. The DNA segment Bam-E-E-D contains three contiguous repeated segments of approximately 5600 base pairs. 3. Each repeated segment can code for an rRNA gene (16-S and 23-S).

The Euglena gracilis chloroplast genome: analysis by restriction enzymes

1. Chloroplast DNA was isolated from autotrophically and mixotrophically grown Euglena gracilis cells. 2. Aliquots of chloroplast DNA were mechanically degraded to an average molecular weight of 4-7 X 10(6) and G+C-rich DNA fragments (density 1.701 g/cm3) were separated from the bulk DNA (density 1.685 g/cm3) using preparative CsCl density gradients. 3. Total chloroplast DNA and its DNA subfractions, which first were characterized with respect to average G+C content and hybridization capacity for chloroplast rRNA, were hydrolysed with restriction endonucleases (endo R-EcoRI, end R-HindII, endoR-HindIII, endo R-HindII+III, endoR-Hpal, endo R-HpaII and endoR-HaeIII). The fragments were separated on gels under a variety of electrophoretic conditions. 4. With each enzyme tested, a rather large number of bands was obtained. In all cases, different banding patterns were obtained for total DNA, and the DNA subfractions. 5. Chloroplast DNA from autotrophically and mixotrophically grown cells gave identical banding patterns. 6. Digestion of total DNA with the endoR-HaeIII yielded 51-52 fragments separated in the gels in a total of 36 bands of which 11-12 bands were composed of 2-3 fragments as estimated by densitometry. The molecular weights of all fragments combined was 87 X 10(6) or 95% of the genome (92 X 10(6)). 7. Chloroplast RNA hybridized to 5.1% with total chloroplast DNA, equal to three RNA cistrons per genome (Mr92 X 10(6)). These cistrons are located on seven different types of endo R-HaeIII fragments. The hybridising fragments are preferentially found in the G+C-rich subfraction and in bands which are composed of 2-3 fragments.

Light-stimulated synthesis of chloroplast DNA

Light-stimulated chloroplast DNA synthesis was studied during chloroplast development in the absence of cell division and nuclear DNA synthesis. Incorporation of 32Pi was stimulated 10-15 fold, however, the ratio of chloroplast DNA to nuclear DNA remained constant. Isotope dilution experiments suggested that stimulated labeling of chloroplast DNA represented more efficient utilization of exogenously supplied Pi rather than stimulated turnover of chloroplast DNA. The low level of DNA synthesis and chloroplast development were resistant to nalidixic acid which inhibits semiconservative replication of chloroplast DNA.

The chloroplastic DNA of Chlorella pyrenoidosa (Emerson strain): heterogeneity and complexity

The heterogeneity and the complexity of Emerson strain Chlorella pyrenoidosa chloroplastic DNA have been investigated by means of thermal denaturation and renaturation kinetics, and the results have been compared with those of the strain 211/8b of the same alga. The thermal denaturation properties are very close to those of the other strain: the Tm of 65 degrees C in 0.1 standard saline citrate, the maximal hyperchromicity of 41%, and the dispersion coefficent delta 2/3 of 6.65 degrees C. The first derivated curves of the melting profiles show also five components. Denatured chloroplastic DNA renatures rapidly. Two fractions are found; their kinetic complexities have been estimated: 1.5 times 10(7) daltons for the fast renaturing fraction; 2x 10(8) daltons for the low d (G + C) content of the chloroplastic DNA: 1.24 times 10(8) daltons). The unique nucleotide sequence is present in about 19 copies per chloroplastic genome. This report confirms the homogeneity of the chloroplastic genome of algae.