in air2p proteins, the fourth and fifth zinc knuckle have different roles. the fourth zinc knuckle have a role in rna binding while the fifth knuckle is important for protein-protein interactions. air2p interacts with the central domain of trf4p and polyadenylation activity of trf4p is dependent on this interaction as deletion or mutation of the knuckles hinders the polyadenylation activity. air1p is responsible for inhibiting methylation of npl3p (a protein which is responsible mrna export). air1p/air2p also direct abnormal mrnps to tramp pathway and bring about their degradation.