(The) tRNA genes complementing the rnpA49 mutation in Escherichia coli

Abstract

The rnpA49 mutation is responsible for the thermosensitive C5 protein, the protein component of Escherichia coli RNase P, which results in thermosensi- tivity of RNase P function. The chromosomal DNA region from Brevibacterium albidum that complements the rnpA49 mutation was analysed. The gene capable of complementing the growth of rnpA49 mutant strain at nonpermissive temperature was identified to be the gene for an arginine tRNA with anticodon CCG through a deletion analysis combined with the thermosensitive complementation assay. Since synthesis of the arginine tRNA from the gene harbored in a multicopy plasmid was correlated with the complementation of the rnpA49 mutation, the gene product responsible for complementation of the thermosensitive rnpA49 mutation was shown to be the arginine tRNA (anticodon CCG) of B. albidum. The Northern analysis and primer extension analysis revealed that the tRNA gene contained its own promoter which was functional in E. coli. It was also investigated whether the genes for other tRNAs from E. coli cloned by PCR amplification could complement rnpA49 mutation, and found that the rnpA49 mutation was not complemented by the genes for other tRNAs except for the gene for the E. coli arginine tRNA (anticodon CCG). This result suggests that only the arginine tRNA (anticodon CCG) either from B. albidum or from E. coli when overproduced from multicopy plasmids can complement the thermosensitive rnpA49 mutation. A plausible explanation was discussed about why the genes for the arginine tRNAs recognizing rare codon CGG were able to complement the growth of rnpA49 mutation at the nonpermissive temperature.