Marker and promoter effects on heterologous expression in Aspergillus nidulans

To study the effects of selection marker, promoter type, and copy number on heterologous expression in Aspergillus nidulans, strains were constructed with single- and multicopy plasmid integrations bearing a reporter gene (lacZ) under the control of either an inducible (alcA) or constitutive (gpdA) promoter and one of three Aspergillus nutritional marker genes (argB, trpC, or niaD). beta-Galactosidase activity in the transformants varied over three orders of magnitude, with the majority of levels in the range of 5x10(3)-1x10(4) U/mg. Significant differences in mean expression levels were found when comparing single-copy transformants with the same promoter but a different marker. Transformants with the argB marker had the highest average expression, approximately threefold over the trpC or niaD clones. For each promoter, maximal expression for the set was seen in the range of the single-copy clones, implying that increasing the copy number does not reliably increase expression in Aspergillus.

Tissue-specific repression of starvation and stress responses of the Neurospora crassa con-10 gene is mediated by RCO1

The Neurospora crassa con-10 gene is weakly expressed in mycelia but is induced approximately 1000-fold during macroconidiation. Studies of the promoter elements and trans-acting factors that regulate con-10 expression are needed to gain a detailed understanding of developmental regulation. The rco-1 mutant displays a 10-fold elevated basal level of expression of con-10. In contrast to the wild type, con-10 expression in mycelia of the rco-1 mutant was rapidly induced to high levels by starvation for carbon or nitrogen and by heat shock. Although con-10 is developmentally induced late in conidiation, con-10 was inducible by heat shock shortly after exposure of the wild-type mycelium to air. These findings support the view that RCO1 is a cell type-specific repressor of con-10. We propose that inactivation of RCO1 allows developing conidiophores to adjust the timing of con-10 induction in response to stress.

Analysis of two transcription activation elements in the promoter of the developmentally regulated con-10 gene of Neurospora crassa

The con-10 gene of Neurospora crassa is activated during conidiation. CRS-B (conidiation response sequence-B) and CGE (con-10 general enhancer) elements have been proposed to function as sites of transcriptional activation and as possible elements that confer developmental regulation to con-10. In a specific analysis of the roles of these elements we found that two CRS-B elements are necessary for full activation of con-10 during macroconidiation, whereas two CGE elements are functionally redundant, such that a single CGE is sufficient for maximal expression. However, CRS-B and CGE elements are not sufficient for developmental activation of a reporter gene. The CRS-B element was further dissected and one of the CRS-B elements appears to function in repression as well as activation. con-10 is also highly expressed during microconidiation, a different form of asexual sporulation, but we show here that CRS-B elements do not play a significant role in con-10 expression during microconidiation. Both CRS-B elements contribute to basal con-10 expression during mycelial growth. con-10 is also regulated by light, and CRS-B and CGE elements may play minor roles in controlling con-10 expression in response to light.