Characterization of the termini of linear plasmids from Nectria haematococca and their use in construction of an autonomously replicating transformation vector.

The mitochondria of isolate FS37 from Nectria haematococca mating population I (Fusarium solani f. sp. cucurbitae) contain two linear plasmids, pFSC1 and pFSC2, of 9.2 and 8.3 kbp, respectively. Evidence for a protein blocking the 5' termini of these plasmids was obtained from exonuclease digestion experiments. A single protein band with an apparent Mr of 80 K was labeled when the DNA-protein complex of either plasmid was reacted with [125I] Bolton-Hunter reagent and then digested with DNase I. DNA sequence analysis of the termini of both plasmids revealed long inverted repeats of 1,211 bp (pFSC1) and 1,027 bp (pFSC2). No sequence similarity was found between the terminal inverted repeats (TIRs) of pFSC1 and pFSC2, nor was any similarity identified between the TIRs of these plasmids and sequences of TIRs from other linear DNAs. A restriction fragment containing the TIR of pFSC1 conferred autonomous replication when incorporated into an integrative transformation vector of Ustilago maydis.