Ribosomal DNA satellite of Euglena gracilis chloroplast DNA

Evidence for a novel DNA component in chloroplasts ofEuglena gracilis

“…It was not immediately clear as to whether this heavier DNA was a contaminant of unknown origin, or represented a second type of chloroplast 'chromosome' or was a G+C rich part of the main circular DNA. 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.…”

“…We had reported earlier that the 1.700 g/cc DNA carries the genes for chloroplast 23 S-16 S rRNA [5]. Depending on the amount of heavy DNA component present, a DNA preparation would hybridize up to 6% with rRNA.…”

“…We repeated the hybridization experiments using [3 HI rRNA and either total chloroplast DNA, or the heavy or light DNA component. The hybridization experiments were done as reported earlier [5] and for each DNA sample a saturation curve was established. 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.…”

“…An additional DNA component with a mean buoyant density of 1.700 g/cc was found to be associated with highly purified chloroplasts [5,6]. It was not immediately clear as to whether this heavier DNA was a contaminant of unknown origin, or represented a second type of chloroplast 'chromosome' or was a G+C rich part of the main circular DNA.…”

“…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].…”