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J. Virol., 09 1996, 6169-6179, Vol 70, No. 9
A Abroi, R Kurg and M Ustav
A set of E2 proteins with mutations in the amino-terminal transactivation
domain was made by a scheme called clustered charged-to- alanine scan.
These mutant E2 proteins were tested for expression, stability, and
compartmentalization in cells and for sequence-specific DNA binding, as
well as in functional assays for transcriptional and replicational
activation. We identified four groups of mutants. First, mutants K111A,
K112A, and E176A were unable to activate replication and transcription
because of oligomerization-induced retention of oligomers in the cytoplasm.
Second, although fractions of the mutant proteins E74A and D143A/ R172C
existed in the oligomeric form, they were localized in the nucleus. Certain
fractions of these proteins existed as a dimer able to form a specific
complex and activate replication; however, these proteins were inactive in
transcriptional activation. Third, mutants R37A and D122A were localized in
the nucleus, existed in the dimeric form, supported replication
efficiently, and were severely crippled in transcriptional activation. The
fourth group of mutants did not differ considerably from the wild-type
protein. The activation of transcription by the wild type as well as mutant
E2 proteins was dependent on the concentration of input E2 expression
vector DNA and had a bell-like shape. We suggest that the reduction of
transcriptional activation at higher E2 concentrations, the self-squelching
activity, is caused by oligomerization of the E2 transactivator and is one
of the mechanisms for the regulation of E2 activity. Our results also show
that transcriptional and replicational activation activities are encoded by
different determinants in the E2 protein.
Copyright © 1996, American Society for Microbiology
Transcriptional and replicational activation functions in the bovine papillomavirus type 1 E2 protein are encoded by different structural determinants
Department of Microbiology and Virology, Tartu University and Estonian Biocentre, Estonia.
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