Toward a transcriptional map of the turkey adenovirus 3 (TAdV-3) genome

Turkey adenovirus 3 (TAdV-3), Siadenovirus gallopavotertii, historically referred to as turkey haemorrhagic enteritis virus (THEV), causes immunosuppression and haemorrhagic enteritis in turkey poults. Although an avirulent TAdV-3 strain is used as a live vaccine, its immunosuppressive properties remain poorly understood at the molecular level. Here, we employed Rapid Amplification of cDNA Ends (RACE) and Sanger sequencing to generate a transcriptomic map of TAdV-3 in infected MDTC-RP19 cells at 24 h post infection. Using RACE and virus-specific primers, we obtained full-length annotation of 14 out of 23 predicted viral transcripts. Analysis of late structural genes revealed a conserved tripartite leader (TPL) sequence shared across all late transcripts, providing new insights into their transcription start sites, splicing events, and promoter architecture. Additionally, we identified alternative leader exons - for instance, DBP mRNA contains a bipartite leader, whereas Hyd mRNA utilizes the TPL - and observed coordinated 3' end processing via shared polyadenylation signals between certain transcripts (e.g. ORF1 and Hyd). This precise annotation of TAdV-3 mRNAs lays the groundwork for linking transcript structure to protein function, enhancing our understanding of TAdV-3's immunosuppressive strategies and informing future development of TAdV-3 based gene delivery platforms.