<p>This family of proteins are about 50 to 77 kDa. The central region is well conserved and contains three conserved histidines. Most of these proteins are related at the N-terminal region to the beta-lactamase family. The family has been charcaterised as ribonuclease J. RNase J cleaves the 5'-leader sequence of certain mRNAs and may play a role in the maturation and stability of specific mRNAs. It is also required for the maturation of the 16S rRNA acting preferentially on 16S rRNA precursors after association of the 30S and 50S ribosomal subunits.</p>