The messenger ribonucleoprotein particle (mRNP) biogenesis is a complex and integrated nuclear process in which a numerous different events are coordinated and coupled. Such events include transcription, pre-mRNA processing (5'end capping, splicing, 3'end cleavage, and poly(A) adition), mRNP formation and export, as well as quality controls. The aberrant transcripts resulting from improper mRNP biogenesis are targeted by the quality control mechanism, causing their retention in the nucleus and degradation by the 3'-5' exoribonuclease Rrp6, which is associated to the exosome. Recently, in our laboratory an inovative assay to study the coupling and coordination between biogenesis and quality control of mRNPs in yeast S. cerevisiae, was implemented. It was shown that bacterial Rho factor, RNA dependent helicase/translocase, functions as a powerful molecular motor that can disrupt RNA-protein complexes present on its path which results with production of full length yet aberrant transcripts. In accordance to currently results which show that Rat1p is involved in a new 5' end quality control, we wanted to test the involvement of possible Rat1p cofactors, Rai1 and Dxo1 proteins, in this new surveillance mechanism. In this work we used properties of the Rho factor to produce improperly processed mRNPs, and showed directly by ChIP experiment that Rat1 homolog, Rai1p, is involved in this quality control. Suprisingly we found that two structural homologs , Rai1 and Dxo1, are not redundant.