Transfer ribonucleic acid genes in the chloroplast deoxyribonucleic acid of pea leaves

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Abstract
The saturation hybridization between pea c[chloroplast]DNA and 125I-labeled pea ct-tRNAs showed that 1.2% of the peak ctDNA codes for tRNA genes. The observed level of hybridization resulted from specific base pairings between ctDNA and ct-RNA as shown by competition hybridization experiments and thermal stability studies on DNA-tRNA hybrids. The level of hybridization obtained in this study amounts to the presence of .apprx. 40 tRNA genes in pea ctDNA. The tRNAs from the cytoplasm of the pea leaves, Escherichia coli, yeast, and calf thymus did not compete with the pea ct-RNAs for the common base sequences in pea ctDNA. The presence of 17 aminoacyl-tRNA synthetases and their corresponding tRNAs was demonstrated in chloroplast. The acylation of ct-tRNAs proceeds with the same rate whether one partially purified tRNA synthetases from chloroplasts of E. coli are used. The aminoacylation of the 3 amino acids glutamic acid, glutamine and cysteine proceeded very slowly in chloroplasts. The individually labeled amino-acyl-tRNAs hybridized with pea ctDNA. The hybridization follows true saturation rates, and the melting profiles of aminoacyl-tRNA-ctDNA indicate the formation of specific base pairs between the ctDNA and tRNA. Seventeen aminoacyl-tRNA genes were identified in the pea ctDNA.

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