3'UTR of ALV-J can affect viral replication through promoting transcription and mRNA nuclear export.

3' Untranslated regions (3'UTRs) play a crucial role in gene transcription and post-transcriptional regulation. During the past 30 years, subgroup J avian leukosis virus (ALV-J) had accumulated large-scale mutations in 3'UTRs of their proviral genome. In this study, we summarize five kinds of mutant 3'UTRs in ALV-J and analyzed their potential functions. Results indicated that ALV-J strains containing different 3'UTRs showed different replication ability, while this divergence is tissue preferential, especially in chicken embryonic liver cells and chicken endothelial cells. All 3'UTRs can assist intron-containing viral mRNA nuclear export, with no salient differences among the five forms. The half-life of ALV-J mRNA is not influenced by different 3'UTRs. However, 3'UTRs can drastically boost mRNA transcription in a cell-specific manner. These different 3'UTRs can promote foreign genes expression. Our results provide novel insight into the pathogenicity and life cycle of ALV-J.IMPORTANCE3'UTRs can affect gene transcription and post-transcriptional regulation in multiple ways, further influencing the function of proteins in a unique manner. Recently, ALV-J has been mutating and evolving rapidly, especially the 3'UTR of viral genome. Meanwhile, clinical symptoms caused by ALV-J have changed significantly. In this study, we found that the ALV-J strains containing △-r-TM-type 3'UTR are the most abundant. By constructing ALV-J infectious clones and subgenomic vectors containing different 3'UTRs, we prove that 3'UTRs directly affect viral tissue preference and can promote virus replication as an enhancer. ALV-J strain containing 3'UTR of △-r-TM proliferated fastest in primary cells. All five forms of 3'UTRs can assist intron-containing viral mRNA nuclear export, with similar efficiency. ALV-J mRNA half-life is not influenced by different 3'UTRs. Our results dissect the roles of 3'UTR on regulating viral replication and pathogenicity, providing novel insights into potential anti-viral strategies.