The Nonautonomous Elements

Routinely, cytoplasmic linear plasmids occur as systems in which an autonomous element is accompanied by one or more nonautonomous attendants (Table 2), some of which encode their own DNA polymerase (pGKL1, pDHL1, pPin1-3, and pDH1A), while others are lacking such genes (pPE1A, pPac1-2, pWR1A) (Hishinuma et al. 1984; Stark et al. 1984; Sor and Fukuhara 1985; Cong et al. 1994; Fukuda et al. 1997; Klassen et al. 2002, 2004; Klassen and Meinhardt 2003). As already mentioned, the DNA polymerases of the pGKL system specifically replicate their own linear plasmid (Kitada and Gunge 1988; Schaffrath et al. 1995), consistent with different TPs of autonomous and nonautonomous elements. Such a scenario may also be realized in the pDHL, pPin, and pDH1 systems. Irrespective of the DNA poly-merases, a nonautonomous plasmid not only depends on the corresponding autonomous element in terms of cytoplasmic replication (SSB, TRF) but also in transcription (RNA polymerase, helicase, and capping enzyme; see above). An obvious function of nonautonomous elements is evident in the killer systems, as they typically encode a protein toxin as well as the respective immunity function, the latter safeguarding the killer strain against its own toxin.

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