Methods are described for improvement of the serum half life of therapeutic nucleic acids by 3′ conjugation to useful target proteins, or other large molecules with useful function. In one embodiment, a 3′ A, C or G overhang is added to ds-DNA and the primary amines conjugated using biocompatible bifunctional linkers to proteins. The resulting nucleic acid-3′ conjugates are serum nuclease-resistant and retained in vivo for long periods without rapid kidney clearance. Further, the choice of conjugate imparts additional functionality to the nucleic acid-3′ conjugate.