ABSTRACT
The genetic trait in mitochondria was first identified as DNA in 1963. The petite mutation and other extranuclearly inherited phenotypes in fungi have been demonstrated to result from alterations of the standard mitochondrial (mt) DNA. These al terations lead in several cases to the formation of mitochondrial plasmids, which are able to replicate autonomously. The mitochondrial DNA (mtDNA) of fungi is usually a covalently closed circular (ccc) molecule. An exception is the linear mtDNA of the yeast Hansenula mrakii. In addition to coding for a limited number of gene products, the mt genomes contain at least one nucleotide sequence recognized by mitochondrial DNA polymerase as an origin of replication. The expression of the genetic information proceeds in several steps which depend on the gene product and on gene organization. The DNA sequence of a gene is first transcribed to a RNA sequence, which is thereafter processed to the mature mRNA or to a mature gene product (rRNA; tRNA).
