A nuclear RNA-binding cyclophilin in human T cells.

Cyclophilins (CyPs) are binding proteins for the immunosuppressive drug cyclosporin A (CsA). CyPs are evolutionarily highly conserved proteins present in both pro- and eukaryotes as well as in different subcellular locations. CyPs possess enzymatic activity, namely peptidyl-prolyl cis-trans isomerase (PPIase) activity; CyPs are involved in cellular protein folding and protein interactions. To date, only cyclosporins and proteins are known to interact with CyPs. Here we describe a novel nuclear cyclophilin (hCyP33) from human T cells with an additional RNA-binding domain. This combines for the first time RNA binding and protein folding in one protein.