NRS1, A REPETITIVE ELEMENT LINKED TO PISATIN DEMETHYLASE GENES ON A DISPENSABLE CHROMOSOME OF NECTRIA-HAEMATOCOCCA

We have identified a repetitive DNA element in Nectria haematococca ma ting population VI, isolate T-2. This repetitive sequence has been cal led Nrs1. DNA hybridization analysis indicates the sequence is found i n several isolates of the fungus pathogenic to Pisum sativum. A 2,027- bp clone containing the Nrs1-2 allele contains a long polyA sequence, imperfect RNA polymerase III promoter sequences, multiple inverted rep eats, and the potential for extensive secondary structure similar to k nown RNA polymerase III transcripts and related retroelements. Ten of the 11 HindIII restriction fragments from isolate T-2 DNA that hybridi ze to Nrs1-2 segregate in a manner consistent with a 1:1 ratio for ran dom ascospore progeny, The 10 restriction fragment length polymorphism (RFLP) loci define three linkage groups and correspond to three chrom osome-sized DNAs from T-2 separated by pulsed field gel electrophoresi s. Three RFLP loci defined by hybridization to the gene for pisatin de methylase and localized on the 1.6 million base pair (Mb) chromosome w ere genetically linked to each other and to several Nrs1 loci. These s equences recombined despite the fact that no obvious homolog exists fo r the 1.6-Mb chromosome in one parent strain. Allelic RFLPs correspond ing to the gene sequence of cutinase were unlinked to Nrs1 loci.