The Synthesis of Chloroplast High-Molecular-Weight Ribosomal Ribonucleic Acid in Spinach

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Abstract
Illuminated suspensions of chloroplasts isolated from young spinach leaves show incorporation of [3H]uridine into several species of RNA. One RNA species of MW 2.7 .times. 106 shows sequence homology with both the chloroplast 23-S rRNA (MW = 1.05 .times. 106) and 16-S rRNA (MW = 0.56 .times. 106), as judged by DNA/RNA competition hybridization. Leaves labeled in vivo with [32P]orthophosphate in the presence of chloramphenicol accumulate labeled RNA of MW 1.28 .times. 106, 0.71/0.75 .times. 106 and 0.47 .times. 106. The 1.28 .times. 106-MW RNA showd 80.5% sequence homology with the 1.05 .times. 106-MW rRNA and the 0.71/0.75 .times. 106-MW RNA mixture shows 76% sequence homology with the 0.56 .times. 106-MW rRNA. Apparently the pathway of rRNA maturation in spinach chloroplasts is similar to Escherichia coli.