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.