The 5\u2032UTR in human adenoviruses: leader diversity in late gene expression

Mirja Ramke,James Chodosh,David W Dyer,Jaya Rajaiya,Jeong Yoon Lee,Donald Seto

doi:10.1038/s41598-017-00747-y

Abstract

Human adenoviruses (HAdVs) shut down host cellular cap-dependent mRNA translation while initiating the translation of viral late mRNAs in a cap-independent manner. HAdV 5′ untranslated regions (5′UTRs) are crucial for cap-independent initiation, and influence mRNA localization and stability. However, HAdV translational regulation remains relatively uncharacterized. The HAdV tripartite leader (TPL), composed of three introns (TPL 1–3), is critical to the translation of HAdV late mRNA. Herein, we annotated and analyzed 72 HAdV genotypes for the HAdV TPL and another previously described leader, the i-leader. Using HAdV species D, type 37 (HAdV-D37), we show by reverse transcription PCR and Sanger sequencing that mRNAs of the HAdV-D37 E3 transcription unit are spliced to the TPL. We also identified a polycistronic mRNA for RID-α and RID-β. Analysis of the i-leader revealed a potential open reading frame within the leader sequence and the termination of this potential protein in TPL3. A potential new leader embedded within the E3 region was also detected and tentatively named the j-leader. These results suggest an underappreciated complexity of post-transcriptional regulation, and the importance of HAdV 5′UTRs for precisely coordinated viral protein expression along the path from genotype to phenotype.

Highlights

Human adenoviruses (HAdVs) shut down host cellular cap-dependent mRNA translation while initiating the translation of viral late mRNAs in a cap-independent manner
By Clustal Omega comparison, we found differences between BPL1-2 and tripartite leader 1 (TPL1)-3 ranging from 41.24% (MAV-2 vs. HAdV-A12) to 45.88% (MAV-2 vs. HAdV-B3 and -E4) (Table 4)
Published work indicates that 5′ untranslated regions (5′untranslated region (UTR)) have significant functional consequences for the regulation of mammalian and viral genes; GC content, length, and secondary structure impact mRNA stability, nuclear export, and translation initiation[24, 43]

Summary

Introduction

Human adenoviruses (HAdVs) shut down host cellular cap-dependent mRNA translation while initiating the translation of viral late mRNAs in a cap-independent manner. A potential new leader embedded within the E3 region was detected and tentatively named the j-leader These results suggest an underappreciated complexity of post-transcriptional regulation, and the importance of HAdV 5′UTRs for precisely coordinated viral protein expression along the path from genotype to phenotype. Viruses, inhibit initiation of host cell 5′ cap-dependent mRNA translation[19], in favor of viral late gene expression in a cap-independent manner, and requiring the viral 5′UTR. Despite the 5′UTR’s significance in translation initiation and post-transcriptional regulation, a comprehensive analysis of the HAdV 5′UTRs has not been performed, and only 6 out of 72 HAdV types available in GenBank have the TPL annotated. We annotated the TPL sequences in all 72 HAdV genotypes, and performed RT-PCR and Sanger sequencing to characterize late mRNAs of the clinically important virus, HAdV-D37. We present the first comprehensive analysis of the 5′UTRs of HAdV types

Methods

Results

Conclusion