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Journal of Virology, June 2006, p. 5423-5434, Vol. 80, No. 11
0022-538X/06/$08.00+0 doi:10.1128/JVI.02585-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Anja Berndt,1
Nina Tavalai,1
Regina Mueller,1
Ursula Schlötzer-Schrehardt,2 and
Thomas Stamminger1*
Institute of Clinical and Molecular Virology, University of Erlangen-Nuernberg, Schlossgarten 4, 91054 Erlangen, Germany,1 Department of Ophthalmology, University of Erlangen-Nuernberg, Schwabachanlage 6, 91054 Erlangen, Germany2
Received 13 December 2005/ Accepted 10 March 2006
We previously showed that open reading frame (ORF) UL26 of human cytomegalovirus, a member of the US22 multigene family of betaherpesviruses, encodes a novel tegument protein, which is imported into cells in the course of viral infection. Moreover, we demonstrated that pUL26 contains a strong transcriptional activation domain and is capable of stimulating the major immediate-early (IE) enhancer-promoter. Since this suggested an important function of pUL26 during the initiation of the viral replicative cycle, we sought to ascertain the relevance of pUL26 by construction of a viral deletion mutant lacking the UL26 ORF using the bacterial artificial chromosome mutagenesis procedure. The resulting deletion virus was verified by PCR, enzyme restriction, and Southern blot analyses. After infection of human foreskin fibroblasts, the UL26 deletion mutant showed a small-plaque phenotype and replicated to significantly lower titers than wild-type or revertant virus. In particular, we noticed a striking decrease of infectious titers 7 days postinfection in a multistep growth experiment, whereas the release of viral DNA from infected cells was not impaired. A further investigation of this aspect revealed a significantly diminished stability of viral particles derived from the UL26 deletion mutant. Consistent with this, we observed that the tegument composition of the deletion mutant deviates from that of the wild-type virus. We therefore hypothesize that pUL26 plays a role not only in the onset of IE gene transcription but also in the assembly of the viral tegument layer in a stable and correct manner.
Present address: Institut für Infektionsmedizin, Universitätsklinikum Schleswig-Holstein Campus Kiel, Brunswiker Str. 4, 24105 Kiel, Germany.
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