Versaw W K, Metzenberg R L
Department of Biomolecular Chemistry, University of Wisconsin, Madison 53706, USA.
Genetics. 1996 Feb;142(2):417-23. doi: 10.1093/genetics/142.2.417.
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.
先前已针对三种粗糙脉孢菌磷酸可阻遏基因描述了一种导致激活因子非依赖性基因表达的转基因位置效应。我们报告了另外两个正调控基因qa-2+和ars-1+的类似发现，表明这种位置效应并不局限于参与磷代谢的基因。此外，我们鉴定了许多表现出激活因子非依赖性基因表达的突变体。这些突变体中的每一个都包含一种染色体重排，其一个断点位于受影响基因的5'上游区域。这表明这些重排与激活因子非依赖性基因表达相关，并且这些顺式作用突变可能代表一种类似于使一些转基因独立于其转录激活因子的位置效应。我们认为，粗糙脉孢菌中的正调控基因通常通过一种顺式作用机制保持在转录抑制状态，直到被特异性激活。通过转化随机整合基因或通过染色体重排破坏这种顺式作用机制，会使这些基因独立或部分独立于它们正常依赖的转录激活因子。
