Characterization of Inverted Repeat Sequences and Ribosomal RNA Genes of Chloroplast DNA from Chlorella Ellipsoidea

Chloroplast DNA isolated from a green alga Chlorella was shown by agarose gel electrophoresis and electron microscopy to contain a pair of large inverted repeat sequences of ca. 23 kbp. Electron microscopy revealed that the repeats were separated from each other by a small single strand loop of 29.5 kbp and a large single strand region of 98.5 kbp.Digestion with the restriction endonucleases Kpnl, Sstl, and Xhol, and hybridization with (32)P-labelled tobacco rDNAs revealed that the genes for 16S and 23S rRNAs are present in the repeated sequences. From the hybridization pattern, a restriction map around the sequences were constructed, and the rRNA genes were found to be on the 10.8 kbp SstI fragment. This location was supported by electron microscopy (R-loop formation).Unlike Chlamydomonas reinhardii, Chlorella lacks a large intron in its 23S rRNA gene, and the 16S-23S spacer region is considerably long; the organization of rRNA operon is similar to that of higher plants.