Rescue of recombinant Newcastle disease virus: current cloning strategies and RNA polymerase provision systems.

Since the first rescue of a recombinant Newcastle disease virus (rNDV) in the late 1990s, many more rNDVs have been rescued by researchers around the world. Regardless of methodology, the main principle behind rescue of the virus has remained the same, i.e., the formation of a functional replication complex by simultaneously providing the full-length viral RNA and the viral NP, P and L proteins. However, different strategies have been reported for the insertion of the full-length genome into a suitable transcription vector, which remains the most challenging step of the rescue. Moreover, several systems have been published for provision of the DNA-dependent RNA polymerase, which is needed for transcription of viral RNA (vRNA) from the transfected plasmid DNA. The aim of this article is to consolidate all of the current cDNA assembly strategies and transcription systems used in rescue of rNDV in order to attain a better understanding of the advantages and disadvantages of each approach.