A CYTIDINE DEAMINASE EXPRESSED IN THE POST-INFECTIVE L3 STAGE OF THE FILARIAL NEMATODE, BRUGIA-PAHANGI, HAS A NOVEL RNA-BINDING ACTIVITY

A number of genes have been identified that are highly expressed in th e post-infective 1.3 stage of the filarial parasite, Brugia pahangi. A mongst these was a cDNA with homology to the cytidine deaminase (CDD) gene family. Phylogenetic analysis of the various cytosine nucleoside deaminases suggest that Brugia pahangi CDD evolved with significant di vergence from the RNA editing family. In order to characterize its fun ction, we have expressed Brugia pahangi CDD in bacteria as a chimera w ith maltose-binding protein (MBP). Biochemical analysis demonstrates t he MBP-CDD fusion protein functions as an authentic cytidine deaminase with an obligate requirement for zinc. In addition to cytidine deamin ase activity, however, the fusion protein demonstrates RNA binding act ivity with specificity for AU-rich sequences and was found to bind an RNA template spanning the edited site of mammalian apolipoprotein B (a poB) mRNA. This RNA binding activity was not found in two different re combinant bacterial CDD proteins. In vitro RNA editing assays revealed that MBP-CDD failed to mediate cytidine deamination of a mammalian ap oB RNA template. Furthermore, binding of MBP-CDD to the apoB RNA did n ot inhibit in vitro editing of this template by apobec-1. The data sug gest that the cytosine nucleoside deaminases and RNA editing deaminase s have acquired different mechanisms of binding to an AU-rich RNA temp late, presumably with different functional implications. (C) 1997 Else vier Science B.V.