Maturation of chloroplast and cytoplasmic ribosomal RNAs from single large precursors in two algal species,Cyanidium andChlorella

Abstract

In the present study the synthesis and the processing of cytoplasmic and chloroplast rRNAs of the algaeCyanidium caldarium (Rhodophyceae),Chlorella pyrenoidosa andChlorella vulgaris (Chlorophyceae) are characterized. The results of pulse-labeling of the cells under autotrophic and heterotrophic conditions, of kinetic analyses of labeling and of pulse-chase experiments demonstrate that the mature chloroplast ribosomal RNAs arise from a single large precursor with an apparent molecular weight of 1.8×106 daltons. For detection of this primary transcript inChlorella lowering of the temperature to 15°C during pulse-labeling was mandatory. The findings also show that it is processed to form the mature species via immediate precursors of about 1.2×106 and 0.59×106 daltons. These results are reinforced by those of additional experiments which were performed in the presence of rifampicin or in which colorless mutant cells ofChlorella vulgaris were studied.