Characterization of mammalian NEF-sp as a testis-specific nuclear 3′→5′ exoribonuclease

Ribonucleases catalyse maturation of functional RNAs or mediate degradation of cellular transcripts, activities that are critical for gene expression control. Here we identify a previously uncharacterized mammalian nuclease family member NEF-sp (LOC81691) as a testis-specific factor. Recombinant human NEF-sp demonstrates a divalent metal ion-dependent 3′→5′ exoribonuclease activity. This activity is specific to single-stranded RNA substrates and is independent of their length. Presence of a 2′-O-methyl modification at the 3′ end of the RNA substrate is inhibitory. Ectopically-expressed NEF-sp localizes to the nucleolar/nuclear compartment in human cell cultures and this is dependent on an N-terminal nuclear localization signal. Finally, mice lacking NEF-sp are viable and display normal fertility, likely indicating overlapping functions with other nucleases. Taken together, our study provides the first biochemical and genetic exploration of the role of the NEF-sp exoribonuclease in the mammalian genome. Testicular transcriptome of Nef-sp-/- and Nef-sp+/- mice was analyzed using RNA-Seq.