RECOMBINANT MITOCHONDRIAL PLASMIDS IN NEUROSPORA COMPOSED OF VARKUD AND A NEW MULTIMERIC MITOCHONDRIAL PLASMID

A mitochondrial plasmid, V5124, in Neurospora intermedia isolate 5124 has a deletion in its sequence relative to the highly similar Mauricev ille and Varkud plasmids. These insertions in the latter plasmids are 28 bp in length and are positioned at sites that correspond to their m ajor transcript 5' termini. The 28-bp sequence is nearly identical to a putative processing site upstream of the ND4L gene on the mitochondr ial genome. The absence of this 28-bp sequence in V5124 apparently res ults in transcripts whose 5' termini correspond to an upstream consens us promoter sequence. Two variant forms of V5124 coexist with V5124 an d have either of two similar 0.3-kb inserts positioned exactly as is t he 28-bp insert in Varkud. These long inserts are chimeric, partly der iving from a newly discovered multimeric plasmid, MP. MP has significa nt similarity to a short region of the mitochondrial satellite plasmid VS. Another part of the 0.3-kb inserts in V5124 variants derives from the mitochondrial genome, within restriction fragment EcoRI-8. Neuros pora mitochondria in many isolates can have several types of mitochond rial plasmids belonging to different homology groups. We propose that a common ancestral plasmid acquired insertions from either the mitocho ndrial genome or from other plasmids. The V5124 variants are the first instance of a chimeric mitochondrial plasmid in which distinct plasmi ds have recombined. This recombination proves that different plasmids coexist currently, or else did so at some point in their evolution, wi thin a single mitochondrion.