The 5'-terminal guanylate of chloroplast histidine tRNA is encoded in its gene.

Among tRNA species histidine tRNAs possess the unique feature of having an additional nucleotide, a guanylate, at their 5'-end. In prokaryotes this G is encoded in the gene sequence and retained in the mature tRNA as result of an unusual cleavage by RNase P (Orellana, O., Cooley, L., and Söll, D. (1986) Mol. Cell. Biol. 6, 525-529), while in eukaryotes it is added post-transcriptionally by a special tRNA guanylyl transferase (Cooley, L., Appel, B., and Söll, D. (1982) Proc. Natl. Acad. Sci. U. S. A. 79, 6475-6479). Here we show that the additional G of chloroplast tRNAHis species is gene-encoded and retained in the tRNA by a processing step analogous to the prokaryotic one. However, the structural requirements for recognition by the different RNase P activities are not the same.