The metallo-beta-lactamase fold contains five sequence motifs. The first four motifs are found in Pfam:PF00753 and are common to all metallo-beta-lactamases. This, the fifth motif [1], appears to be specific to Zn-dependent metallohydrolases such as ribonuclease J 2 [4] which are involved in the processing of mRNA [2,3]. This domain adds essential structural elements to the CASP-domain and is unique to RNA/DNA-processing nucleases, showing that they are pre-mRNA 3'-end-processing endonucleases [2,3,4].

1: Metallo-beta-lactamase fold within nucleic acids processing enzymes: the beta-CASP family. Callebaut I, Moshous D, Mornon JP, de Villartay JP; Nucleic Acids Res 2002;30:3592-3601. PMID:12177301

2: Polyadenylation factor CPSF-73 is the pre-mRNA 3'-end-processing endonuclease. Mandel CR, Kaneko S, Zhang H, Gebauer D, Vethantham V, Manley JL, Tong L; Nature. 2006;444:953-956. PMID:17128255

3: Crystal structure of an archaeal cleavage and polyadenylation specificity factor subunit from Pyrococcus horikoshii. Nishida Y, Ishikawa H, Baba S, Nakagawa N, Kuramitsu S, Masui R; Proteins. 2010;78:2395-2398. PMID:20544974

4: Characterization of components of the Staphylococcus aureus mRNA degradosome holoenzyme-like complex. Roux CM, DeMuth JP, Dunman PM; J Bacteriol. 2011;193:5520-5526. PMID:21764917