Linear kalilo DNA is a Neurospora mitochondrial plasmid that integrates into the mitochondrial DNA

The linear autonomous form of kalilo DNA (previously called AR-kalDNA) is shown to be resident within mitochondria rather than nuclei, as had been suggested by previous experiments. This form has been renamed mtAR-kalDNA, to signify its mitochondrial location. Experiments are described that illustrate the inheritance and somatic transmission patterns of the mitochondrial kalilo plasmid and the mitochondrial inserted form of kalilo DNA (mtlS-kalDNA). Progeny of a cross with a pre-senescent subculture as the female parent inherited mtAR-ka1DNA only; mtIS-kalDNA was not transmitted sexually. During somatic propagation of the ascospore cultures, novel kalilo DNA inserts appeared and most of them persisted until death. We propose that these inserts originated from de novo integration of mtAR-kalDNA into the mitochondrial DNA. In two of the ascopore-derived series analyzed, the first inserts detected were seen only transiently and inserts appearing subsequent to the transient inserts were retained until death. We propose that these enduring inserts originated either from rearrangements of the transient inserts or from novel integration events, either from mtAR-kalDNA or from transposition of the transient inserts.