Mol. Cell. Biol., 10 1997, 6191-6201, Vol 17, No. 10
J Wu and BL Miller
The Stunted protein (StuAp) is a member of a family of transcription
factors that regulate fungal development and cell cycle progression.
Regulated stuA gene expression is required for correct cell pattern
formation during asexual reproduction (conidiation) and for initiation of
the sexual reproductive cycle in Aspergillus nidulans. Transcriptional
initiation from two different promoters yields overlapping mRNAs (stuA
alpha and stuAbeta) that upon translation yield the same protein. Here we
show that multiple regulatory mechanisms interact to control (i)
developmental competence-dependent expression of both transcripts and (ii)
induction-dependent expression of stuA alpha, but not stuAbeta, by the
conidiation-specific Bristle (BrlAp) transcriptional activator.
Quantitative levels of both mRNAs are further modulated by (i) an
activator(s) located at a far-upstream upstream activation sequence, (ii)
feedback regulation by StuAp, and (iii) positive translational regulation
that requires the peptide product of a micro-open reading frame unique to
the stuA alpha mRNA 5' untranslated region. Gradients in stuA alpha
expression were most important for correct cell and tissue type
development. Threshold requirements were as follows: metula-phialide
differentiation < ascosporogenesis < cleistothecial shell-Hulle cell
differentiation. Altered stuA expression affected conidiophore morphology
and conidial yields quantitatively but did not alter the temporal
development of cell types or conidiophore density. By contrast, the sexual
cycle showed both temporal delay and quantitative reduction in the number
of cleistothecial initials but normal morphogenesis of tissue types.
Copyright © 1997, American Society for Microbiology
Aspergillus asexual reproduction and sexual reproduction are differentially affected by transcriptional and translational mechanisms regulating stunted gene expression
Department of Microbiology, Molecular Biology and Biochemistry, University of Idaho, Moscow 83844, USA.
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