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

Abstract

The saturation hybridization between pea ctDNA and 125I-labeled pea ct-tRNAs has shown that 1.2% of the peak ctDNA codes for tRNA genes. The observed level of hybridization has been found to result 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 approximately 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-tRNAs 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 the partially purified tRNA synthetases from chloroplasts of E. coli are used. The aminoacylation of the three amino acids glutamic acid, glutamine, and cysteine proceeded very slowly in chloroplasts. The individually labeled aminoacyl-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 have been identified in the pea ctDNA.

Sequence organization of a pea chloroplast DNA gene coding for a 34,500-dalton protein.

“…and ca. 30 to 40 genes for the tRNAs found in the chloroplast (8,20). The relative abundance and stability of these RNA species facilitated their localization in the higherplant ctDNA.…”

Distribution of transfer RNA genes in thePisum sativum chloroplast DNA

“…tRNA chains of chloroplasts do not share any base sequences with cytoplasmic tRNAs (14). The heterologous hybridization between ctDNA and tRNAs have shown that the genes for tRNAs have undergone much more divergence than that observed for rRNA genes (15).…”

“…The tRNAs for aminoacids cysteine, methionine and glutamine were not detected. The inability to localize the genes for three distinct aminoacyl tRNAs in ctDNA of Zea mays and Pisum sativum probably result from inadequate charging of the tRNAs rather than the lack of their genes in ctDNA (14,20). It was shown that there are about 25 tRNA genes in Euglena gracilis (19).…”

Number of tRNA genes in wheat chloroplast DNA

“…Against the background of this overall similarity there are, however, differences in the size of the 16 S-23 S spacer [7,8] in the positions of restriction sites even among plants of the same genus , in the arrangements of the conserved sequences [9] and in the variable capacity of coding for tRNAs. In pea chloroplast DNA 40 tRNA genes were estimated [12]: 21 in spinach [13], 26 in Euglena [ 14,151 and 40-45 4 S RNA genes were found in duckweed [6]. The chloroplast genome of maize, the only representative of cereals so far investigated with this perspective, has 20-26 tRNA genes [16].…”