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Journal of Virology, May 1999, p. 3800-3809, Vol. 73, No. 5
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Expression and Characterization of a Novel
Structural Protein of Human Cytomegalovirus, pUL25
Maria Concetta
Battista,
Giovanna
Bergamini,
Maria Cristina
Boccuni,
Fabio
Campanini,
Alessandro
Ripalti, and
Maria
Paola
Landini*
Department of Clinical and Experimental
Medicine, Division of Microbiology, University of Bologna, St.
Orsola Hospital, Bologna, Italy
Received 12 October 1998/Accepted 14 January 1999
Human cytomegalovirus (HCMV) UL25 has recently been found to encode
a new structural protein that is present in both virion and defective
viral particles (C. J. Baldick and T. Shenk, J. Virol.
70:6097-6105, 1996). In the present work a polyclonal antibody was
raised against a prokaryotic pUL25 fusion protein in order to
investigate the biosynthesis and localization of the UL25 product (pUL25) during HCMV replication in human fibroblasts. Furthermore, pUL25 was transiently expressed in its native form and fused to the
FLAG epitope, in COS7 and U373MG cells, in order to compare the
properties of the isolated protein and that produced during infection.
Immunoblotting analysis revealed a group of polypeptides, ranging from
80 to 100 kDa, in both transfected and infected cells; in vivo labeling
experiments with infected cells demonstrated they are
posttranslationally modified by phosphorylation. The transcriptional
analysis of the UL25 open reading frame combined with the study of
pUL25 biosynthesis showed true late kinetics for this protein in
infected human fibroblasts. By indirect immunofluorescence both
recombinant and viral pUL25 were detected exclusively in the cytoplasm
of transfected or infected cells. Interestingly, pUL25 was shown to
localize in typical condensed structures in the perinuclear region as
already observed for other HCMV tegument proteins. Colocalization of
ppUL99 in the same vacuoles suggests that these structure are endosomal
cisternae, which are proposed to be a preferential site of viral
particle envelopment. Our data suggest that pUL25 is most likely a
novel tegument protein and possibly plays a key role in the process of envelopment.
*
Corresponding author. Mailing address: Department of
Clinical and Experimental Medicine, Division of Microbiology,
University of Bologna, St. Orsola Hospital, Via Massarenti 9, 40138 Bologna, Italy. Phone: 39-51-341652. Fax: 39-51-341632. E-mail:
viroland{at}med.unibo.it.
Journal of Virology, May 1999, p. 3800-3809, Vol. 73, No. 5
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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