Construction of a shuttle vector for the filamentous fungus Neurospora crassa

We have constructed a recombinant plasmid, pALS-1, that replicates autonomously in both Neurospora and Escherichia coli. pALS-1 consists of the mitochondrial plasmid from Neurospora strain P405-Labelle, the Neurospora qa-2+ gene, and E. coli plasmid pBR325. pALS-1 transforms the Neurospora qa-2+ gene at frequencies 5- to 10-fold higher than those for plasmids that transform mainly by integration. When E. coli was transformed with DNA from Neurospora transformants, we recovered not only pALS-1 but also a smaller plasmid, pALS-2, which had undergone deletion of most and possibly all Labelle sequences, and the immediately flanking sequences in pBR325. pALS-2 also appears to replicate autonomously in Neurospora, but less efficiently than does pALS-1. Southern blots show that free pALS-1 and pALS-2 are present in nuclear and cytosolic (supernatant from high-speed centrifugation) fractions of Neurospora transformants and that small, variable proportions of the plasmids also can be detected in mitochondria. pALS-1 and pALS-2 constitute putative shuttle vectors for Neurospora.