Purification, characterization and biological studies of Escherichia coli exoribonuclease BN

Date of Completion

January 1999


Biology, Molecular|Chemistry, Biochemistry




RNase BN is an E. coli exoribonuclease that was previously shown to be required for the maturation of certain T4 encoded tRNAs. In this study the gene encoding RNase BN, rbn, was mapped to 88 minutes on the E. coli chromosome and subsequently cloned. RNase BN was then overexpressed and purified to near homogeneity. The purified enzyme has a molecular weight of ~65 kDa. RNase BN has a number of unique properties compared to other known exoribonucleases in E. coli. The optimal conditions for activity include a pH of 6.5, the presence of Co 2+, and a monovalent cation. The enzyme is highly specific. It only processes tRNA molecules that contain an incorrect residue within the universal 3‘-CCA sequence. Other tRNA, RNA, and DNA molecules tested thus far are essentially inactive as substrates. tRNA molecules with substitutions within the -CCA sequence are not normally found in E. coli, however, so the role of RNase BN in uninfected cells remains to be determined. ^