TY - JOUR
T1 - An isoform variant of the cytomegalovirus immediate-early auto repressor functions as a transcriptional activator
AU - Baracchini, Edgardo
AU - Glezer, Emilia
AU - Fish, Kenneth
AU - Stenberg, Richard M.
AU - Nelson, Jay A.
AU - Ghazal, Peter
PY - 1992/6
Y1 - 1992/6
N2 - The major immediate-early promoter (MIEP) of human cytomegalovirus directs the expression of several differentially spliced and polyadenylated mRNAs. These mRNAs encode nuclear phosphorproteins (IE55, IE72, and IE86), which consist of common and unique amino acid sequences. To date, very little is known of the functional role of the 55-kDa (IE55) protein. Here we present evidence that the IE55 protein is a positive activator of the MIEP. In human fibroblast cells IE55 protein activated the MIEP between 10- and 30-fold. Fusion of IE55 to the GAL4 DNA binding domain resulted in a chimeric protein capable of trans-activating a reporter with GAL4 recognition sequences. These results strongly suggest that IE55 is a bona fide transcriptional activator protein. In addition, the IE55 protein was found not to act synergistically with the IE72 activator protein. The IE55 protein shares the same amino acid sequence as IE86 except for a 154-amino-acid deletion at the C-terminal end of the protein. These proteins were functionally antagonistic; IE55 relieved repression by IE86 and, conversely, IE86 negated IE55 activation. Mutagenesis of the MIEP revealed that the target sequence for activation by IE55 is different from the IE86 autorepressive response element. These experiments suggest that the mechanism of action of the IE55 and IE86 isoforms is distinct. Moreover, from these results it is apparent that the interplay of these factors might be critical in determining the level of HCMV replication in the host.
AB - The major immediate-early promoter (MIEP) of human cytomegalovirus directs the expression of several differentially spliced and polyadenylated mRNAs. These mRNAs encode nuclear phosphorproteins (IE55, IE72, and IE86), which consist of common and unique amino acid sequences. To date, very little is known of the functional role of the 55-kDa (IE55) protein. Here we present evidence that the IE55 protein is a positive activator of the MIEP. In human fibroblast cells IE55 protein activated the MIEP between 10- and 30-fold. Fusion of IE55 to the GAL4 DNA binding domain resulted in a chimeric protein capable of trans-activating a reporter with GAL4 recognition sequences. These results strongly suggest that IE55 is a bona fide transcriptional activator protein. In addition, the IE55 protein was found not to act synergistically with the IE72 activator protein. The IE55 protein shares the same amino acid sequence as IE86 except for a 154-amino-acid deletion at the C-terminal end of the protein. These proteins were functionally antagonistic; IE55 relieved repression by IE86 and, conversely, IE86 negated IE55 activation. Mutagenesis of the MIEP revealed that the target sequence for activation by IE55 is different from the IE86 autorepressive response element. These experiments suggest that the mechanism of action of the IE55 and IE86 isoforms is distinct. Moreover, from these results it is apparent that the interplay of these factors might be critical in determining the level of HCMV replication in the host.
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U2 - 10.1016/0042-6822(92)90506-K
DO - 10.1016/0042-6822(92)90506-K
M3 - Article
C2 - 1316671
AN - SCOPUS:0026629350
SN - 0042-6822
VL - 188
SP - 518
EP - 529
JO - Virology
JF - Virology
IS - 2
ER -