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Mol. Cell. Biol., 01 1997, 115-122, Vol 17, No. 1
MB Sainz, SA Goff and VL Chandler
C1 is a transcriptional activator of genes encoding biosynthetic enzymes of
the maize anthocyanin pigment pathway. C1 has an amino terminus homologous
to Myb DNA-binding domains and an acidic carboxyl terminus that is a
transcriptional activation domain in maize and yeast cells. To identify
amino acids critical for transcriptional activation, an extensive random
mutagenesis of the C1 carboxyl terminus was done. The C1 activation domain
is remarkably tolerant of amino acid substitutions, as changes at 34
residues had little or no effect on transcriptional activity. These changes
include introduction of helix- incompatible amino acids throughout the C1
activation domain and alteration of most single acidic amino acids,
suggesting that a previously postulated amphipathic alpha-helix is not
required for activation. Substitutions at two positions revealed amino
acids important for transcriptional activation. Replacement of leucine 253
with a proline or glutamine resulted in approximately 10% of wild-type
transcriptional activation. Leucine 253 is in a region of C1 in which
several hydrophobic residues align with residues important for
transcriptional activation by the herpes simplex virus VP16 protein.
However, changes at all other hydrophobic residues in C1 indicate that none
are critical for C1 transcriptional activation. The other important amino
acid in C1 is aspartate 262, as a change to valine resulted in only 24% of
wild-type transcriptional activation. Comparison of our C1 results with
those from VP16 reveal substantial differences in which amino acids are
required for transcriptional activation in vivo by these two acidic
activation domains.
Copyright © 1997, American Society for Microbiology
Extensive mutagenesis of a transcriptional activation domain identifies single hydrophobic and acidic amino acids important for activation in vivo
Institute of Molecular Biology, University of Oregon, Eugene 97403- 1229, USA.
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