LAUSR

Rho-dependent transcription termination is a well conserved process in bacteria. The Psu and YaeO proteins are the two established inhibitors of the ATP-dependent RNA helicase Rho protein of E. coli. Here we show a detailed sequence and phylogenetic analysis demonstrating that V. cholerae YaeO (VcYaeO) is significantly distinct from its E. coli counterpart. VcYaeO induces significant growth defect upon in vivo expression and inhibits in vitro functions of the V. cholerae Rho on directly binding to the latter. Through various biophysical techniques we showed that interaction of VcYaeO disrupts the oligomeric state of the VcRho. Structure of VcYaeO solved at 1.75 Å resolution, the first crystal structure of a YaeO protein, demonstrates a beta-sandwich fold distinct from the NMR-structure of the EcYaeO. Interestingly, VcYaeO structurally resembles the Hfq protein and like the latter it exhibits ssDNA/RNA binding properties. Docking studies demonstrate probable interactions of VcYaeO with VcRho and mode of inhibition of RNA binding to Rho. We propose that VcYaeO inhibits the function of the Rho protein via disruption of the latter's hexameric assembly and also likely by sequestering the RNA from the Rho primary binding sites.