Zusammenfassung
The Drosophila melanogaster E74 gene is induced directly by the steroid
hormone ecdysone and is a member of a small set of "early" genes
that appear to trigger the onset of metamorphosis. The gene consists
of three overlapping transcription units encoding two proteins, E74A
and E74B, which possess a common C terminus. According to the Ashburner
model for ecdysone's action, an E74 protein product potentially functions
as a transcriptional activator of "late" genes as well as a repressor
of early genes. We have taken an evolutionary approach to understand
the function and regulation of E74 by isolating the homologous genes
from Drosophila pseudoobscura and Drosophila virilis and comparing
them to D. melanogaster E74 sequences. Conserved characteristics
of the E74 genes include ecdysone inducibility, localization to ecdysone-induced
polytene chromosome puffs, and gene size. Amino acid sequence comparisons
of the E74A protein reveal a highly conserved C-terminal region that
is rich in basic amino acid residues and which has been proposed
to possess sequence-specific DNA binding activity. The moderately
conserved N-terminal region has maintained its overall acidic character
and is a potential transcriptional activator domain. The central
region contains conserved glutamine and alanine homopolymeric repeats
of variable lengths. Nucleotide sequence comparisons of the E74A
promoter region fail to reveal ecdysone-response elements but do
identify conserved sequences that may function in E74A regulation.
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