The roles of the intergenic sequences (IGS) and untranslated regions (UTR) in Newcastle disease virus (NDV) transcription and pathogenesis are not clear. By our established reverse genetics system, we investigated the role of these noncoding regions in NDV life cycle.

The infectious recombinant viruses containing increased/decreased length of F-HN and HN-L IGS were recovered and the transcription and pathogenicity of mutants were characterized. Our studies indicated that increased F-HN or HN-L IGS length reduced the downstream gene transcription. Morever, all IGS mutants were attenuated in chickens and the level of attenuation was increased as the length of IGS increased.

The mutant viruses with modified 5' and 3' UTR of HN mRNA were also recovered. The transcription, translation and pathogenecity of these recombinant viruses were characterized. Our studies indicated that the UTRs are not essential for NDV replication in vitro. Complete deletions of 5' HN UTR down regulated its transcription, translation levels and incorporation of HN protein into virus particle, therefore, attenuated the pathogenicity of NDV in chickens. Moreover, studies on the HN UTRs replaced with corresponding NP UTRs virus suggested that UTRs can be exchanged between NDV mRNAs without affecting the replication of virus in vitro and in vivo.

In summary, my research identifies for the first time the role of noncoding regions in NDV replication and pathogenesis and provides novel methods for the development of attenuated live vaccines for NDV.