Activator-independent gene expression in Neurospora crassa.
A transgenic position effect that causes activator-independent gene expression has been described previously for three Neurospora crassa phosphate-repressible genes. We report analogous findings for two additional positively regulated genes, qa-2+ and ars-1+, indicating that such position effects are not limited to genes involved in phosphorus metabolism. In addition, we have characterized a number of mutants that display activator-independent gene expression. Each of these mutants contains a chromosomal rearrangement with one breakpoint located in the 5'-upstream region of the affected gene. This suggests that the rearrangements are associated with activator-independent gene expression and that these cis-acting mutations may represent a position effect similar to that responsible for rendering some transgenes independent of their transcriptional activators. We suggest that positively regulated genes in N. crassa are normally held in a transcriptionally repressed state by a cis-acting mechanism until specifically activated. Disruption of this cis-acting mechanism, either by random integration of a gene by transformation or by chromosomal rearrangement, renders these genes independent or partly independent of the transcriptional activator on which they normally depend.
Versaw
W K
WK
Department of Biomolecular Chemistry, University of Wisconsin, Madison 53706, USA.
Metzenberg
R L
RL
D015825:Chromosomes, Fungal; D015966:Gene Expression Regulation, Fungal; D015321:Gene Rearrangement; D009492:Neurospora crassa / Q000235:genetics*; D019076:Transgenes