SOME PROPERTY OF THE NUCLEUS DETERMINES THE COMPETENCE OF NEUROSPORA-CRASSA FOR TRANSFORMATION

In Neurospora, transformation of spheroplasts is quite efficient and u sually occurs with the transforming DNA integrated at ectopic sites in the chromosome. However, only a small fraction of the spheroplasts is actually competent for transformation. To distinguish whether the lim itation to competence is at the level of the plasma membrane or at the level of the nucleus, we performed experiments in which heterocaryoti c spheroplasts were required to integrate two different plasmids in on e transformation procedure. The cotransformants were then analyzed to determine into which nucleus or nuclei the separate plasmids had integ rated. Results of such experiments confirm that successful ectopic tra nsformation in Neurospora crassa requires a competent nucleus. The int egration patterns of the two separate plasmids indicate that the avail ability of appropriate chromosomal sites for ectopic integration may b e an aspect of nuclear competence.