Chloroplast ribosomal RNA genes in the chloroplast DNA of Euglena gracilis

Evidence for a novel DNA component in chloroplasts ofEuglena gracilis

“…The hybridization plateaux were reached at a rRNA-DNA ~g//ag) ratio of 0.4 : 0. chloroplast DNA, heavy fraction DNA and light fraction DNA were 2.8%, 6.9% and 1.1%, respectively. These hybridizations clearly show that the heavy component carries the majority of the rRNA genes which is in line with earlier reports [5,7]. In this particular case, estimating the 1.692 g/cc I)NA to represent about 25-30% of the total DNA (see fig.…”

“…Total chloroplast DNA hybridized to 2.8%. This is significantly higher than the 1.9% reported by Rawson and Haselkom [7]. The only major difference in the two experiments is the starting cell material.…”

“…Most characteristic for this heavy DNA component was its high affinity for chloroplast rRNA as evidenced by DNA-RNA hybridization experiments [5]. Recently, Rawson and Haselkorn [7] working with highly purified total chloroplast DNA confirmed our observations and further showed that some 1.700 g/cc DNA could be generated from total chloroplast DNA by mechanical degradation. They inferred that the 1.700g/cc DNA is a segment of the 44 ~tm long chromosome, carrying the chloroplast rRNA genes.…”

“…However, we show in the following that this 1.692 g/cc DNA is a genuine chloroplast DNA. In particular, evidence is given that the 1.692 g/cc DNA upon shearing yields 1.700 g/cc DNA and that it has a high affinity for chloroplast rRNA similar to the 1.700 g/cc DNA characterized earlier [5,7].…”

Hybridization studies with RNA and DNA isolated from Euglena gracilis chloroplasts and mitochondria

“…Euglena chloroplast DNA (chDNA) was shown to code for 23 S, 16 S rRNA [7][8][9]. The number of cistrons per chromosome, however, is still in doubt and could be between one and three [9][10][11].…”