CHARACTERIZATION OF THE SEQUENCE COMPLEXITY AND ORGANIZATION OF THE NEUROSPORA-CRASSA GENOME

Reassociation kinetic experiments with total DNA and isolated kinetic components are presented that characterize the complexity and organization of sequences in the genome of Neurospora crassa. The genome was found to have a size of 2.7 × 107 nucleotide pairs and to consist of unique (90%), repetitive (8%), and foldback (2%) elements. The arrangement of the repetitive sequences was determined from a variety of studies which examined the properties of long fragments and their reassociation. The results all indicate that Neurospora repetitive sequences are not organized in a short-period in-terspersion pattern. The repetitive DNA occurs in clusters at least 10000 nucleotide pairs long and possibly in considerably longer stretches up to 73 000 nucleotide pairs. The extreme length of the repetitive sequences indicated they are not interspersed in regular intervals with single-copy DNA. As an upper limit, only 0.7% of the single-copy sequences are contiguous with repetitive DNA in fragments 6400 nucleotides in length. These results reveal that Neurospora does not follow either the long- or short-period interspersed pattern, since essentially no interspersed sequences were found. The low complexity of the repetitive component and its reiteration frequency suggest that the repetitive DNA could largely be comprised of ribosomal gene sequences. The lack of interspersed repetitive DNA strongly argues that repetitive DNA does not have a regulatory function in Neurospora. © 1979, American Chemical Society. All rights reserved.