The filamentous fungus Neurospora crassa has been utilized as a model organism for decades, particularly in the fields of genetics and molecular biology. Despite this, Neurospora’s value is diminished by its recalcitrance to expressing most non-native DNA (or heterologous) sequences introduced into its genome. We propose this phenomenon results from previously unidentified regulatory mechanisms encoded within the fungal genome which recognizes and targets these non-native sequences, preventing their expression. We have shown that this mechanism is susceptible to inactivation through mutation. By creating an experimental strain containing inexpressible cas9 sequence fused to native leucine synthesis gene leu-1, we rendered the fungi auxotrophic. Using ultraviolet radiation, mutant transgenic strains are generated and can be screened for heterologous expression positive(hep) mutations using growth assays. Growth rates on culture plates and in race tubes have successfully identified several candidate mutations which will facilitate the future genetic manipulation of Neurospora.