The additional guanylate at the 5' terminus of Escherichia coli tRNAHis is the result of unusual processing by RNase P.

In eucaryotes the 5'-terminal guanylate moiety of mature tRNAHis is added posttranscriptionally. To determine whether the same mechanism occurs in procaryotes, we processed in vitro-derived Escherichia coli tRNAHis precursors to mature tRNA, either in E. coli extracts or by using pure M1-RNA, the catalytic component of RNase P. The results show that the extra guanylate at the 5' end of mature E. coli tRNAHis is encoded in the gene and is found in tRNA as the result of an unusual cleavage by RNase P.