Localization of a r-protein gene within the chloroplast DNA replication origin of Chlamydomonas

In our previous study of chloroplast (Cp) DNA replication in Chlamydomonas reinhardtii, one D-loop site with its flanking regions was cloned and sequenced. The D-loop site mapped by electron microscopy (EM) overlaps with an open reading frame (ORF) potentially coding for a polypeptide of 136 amino acids. In this report, the corresponding D-loop isolated from another species of Chlamydomonas was sequenced. An ORF was also detected. Sequence comparison indicated that most conserved sequences between these two cloned origins are located within the ORF. Amino acid sequences of these two ORFs are highly conserved. The corresponding sequence for this ORF in the tobacco Cp genome was located by a Southern blotting analysis. Since the complete sequence data of Cp DNAs from a liverwort and from tobacco have been determined in 2 Japanese laboratories recently, it has been possible for us to show that this ORF encodes a protein homologous to the Cp ribosomal protein (r-protein) L16, by sequence comparison.