De. Bowles et al., THE ICP0 PROTEIN OF EQUINE HERPESVIRUS-1 IS AN EARLY PROTEIN THAT INDEPENDENTLY TRANSACTIVATES EXPRESSION OF ALL CLASSES OF VIRAL PROMOTERS, Journal of virology, 71(7), 1997, pp. 4904-4914
To assess the role of the equine herpesvirus type 1 (EHV-1) ICP0 prote
in (EICP0) in gene regulation, a variety of molecular studies on the E
ICP0 gene and gene products of both the attenuated cell culture-adapte
d Kentucky A (KyA) strain and the Ab4p strain were conducted. These in
vestigations revealed that (i) the ICP0 open reading frame (ORF) of th
e KyA virus strain is 1,257 bp in size and would encode a protein of 4
19 amino acids, and in comparison to the ICP0 gene (ORF63) of the Ab4p
strain of 1,596 bp (E. A. Telford, M. S. Watson, K. McBride, and A. J
. Davison, Virology 189:304-316, 1992), it lass an internal in-frame d
eletion of 339 bp; (ii) one early transcript of 1.4 kb predicted to en
code the EICP0 protein and a late transcript of 1.8 kb are detected in
Northern blot analysts using probes containing the EICP0 ORF; (iii) t
he Kya EICP0 protein (50 kDa) and the Ab4p EICP0 protein (80 kDa) are
expressed as several species of early proteins that are first detected
at 3 to 4 h postinfection by Western blot analyses of infected-cell p
olypeptides, using an antiserum generated to a TrpE fusion protein tha
t. harbors amino acids 46 to 153 of the EICP0 protein: and (iv) the EI
CP0 protein of both EHV-1 strains is a potent transactivator of EHV-1
genes. Transient expression assays using a simian virus 40 expression
construct of the EICP0 protein of the KyA strain showed that the EICP0
protein independently transactivated chloramphenicol acetyltransferas
e reporter constructs under the control of the immediate early promote
r (3.9-fold), the early thymidine kinase promoter (95-fold), the late
(gamma 1) IR5 promoter (85-fold), and the late (gamma 2 glycoprotein K
promoter (21-fold), The finding that the EICP0 protein of the KyA vir
us can function as an activator of gene expression indicates that amin
o acids corresponding to residues 319 to 431 of the Ab4p EICP0 protein
are not essential for EICP0 transactivation of EHV-1 promoters.