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Open Access Research article

Reannotation of the CELO genome characterizes a set of previously unassigned open reading frames and points to novel modes of host interaction in avian adenoviruses

Stefan Washietl12 and Frank Eisenhaber1*

Author Affiliations

1 Research Institute of Molecular Pathology, Dr. Bohrgasse 7, A-1030 Vienna, Austria

2 Current address: Institute for Theoretical Chemistry and Structural Biology, University of Vienna, Waehringerstrasse 17, A-1090 Vienna, Austria

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BMC Bioinformatics 2003, 4:55  doi:10.1186/1471-2105-4-55

Published: 7 November 2003

Abstract

Background

The genome of the avian adenovirus Chicken Embryo Lethal Orphan (CELO) has two terminal regions without detectable homology in mammalian adenoviruses that are left without annotation in the initial analysis. Since adenoviruses have been a rich source of new insights into molecular cell biology and practical applications of CELO as gene a delivery vector are being considered, this genome appeared worth revisiting. We conducted a systematic reannotation and in-depth sequence analysis of the CELO genome.

Results

We describe a strongly diverged paralogous cluster including ORF-2, ORF-12, ORF-13, and ORF-14 with an ATPase/helicase domain most likely acquired from adeno-associated parvoviruses. None of these ORFs appear to have retained ATPase/helicase function and alternative functions (e.g. modulation of gene expression during the early life-cycle) must be considered in an adenoviral context. Further, we identified a cluster of three putative type-1-transmembrane glycoproteins with IG-like domains (ORF-9, ORF-10, ORF-11) which are good candidates to substitute for the missing immunomodulatory functions of mammalian adenoviruses. ORF-16 (located directly adjacent) displays distant homology to vertebrate mono-ADP-ribosyltransferases. Members of this family are known to be involved in immuno-regulation and similiar functions during CELO life cycle can be considered for this ORF. Finally, we describe a putative triglyceride lipase (merged ORF-18/19) with additional domains, which can be expected to have specific roles during the infection of birds, since they are unique to avian adenoviruses and Marek's disease-like viruses, a group of pathogenic avian herpesviruses.

Conclusions

We could characterize most of the previously unassigned ORFs pointing to functions in host-virus interaction. The results provide new directives for rationally designed experiments.