Extranuclear Inheritance: Virus-Like DNA-Elements in Yeast

Pichia acaciae Killer System: Genetic Analysis of Toxin Immunity

“…The two species each harbor a pair of extranuclear linear plasmids, i.e., pGKL1 (8.9 kb) and pGKL2 (13.5 kb) (K. lactis) and pPac1-1 (13.6 kb) and pPac1-2 (6.8 kb) (P. acaciae) (1,8,37). The larger plasmids are autonomous elements displaying almost identical gene contents that include loci essential for cytoplasmic replication, transcription, and transcript modification (14,15). In contrast, the smaller plasmids carry structurally distinct toxin genes (32); these elements are nonautonomous and rely on the respective larger autonomous plasmid for extranuclear replication and transcription (29).…”

“…The entire nucleotide sequence of the autonomous plasmid pPac1-1 was recently established (14) and consists of no possible candidate gene for PaT immunity, since all genes located on this plasmid are highly conserved among other autonomous plasmids, including pGKL2 (8) and pPE1B (15), which fail to protect against PaT ( Fig. 1 and data not shown).…”

“…73, 2007 P. ACACIAE pPac1-2 ORF4 ENCODES IMMUNITY 4377 (15) killer systems and probably also for the pPac1-2 homologous killer plasmid pWR1A from Debaryomyces robertsiae, in which a pPac1-2 ORF4 homologue is present (22). Thus, the immunity factor constitutes an autoselection system for the nonautonomous element, which can otherwise be accidentally lost (7,40).…”

Yeast Killer Toxins: Fundamentals and Applications

“…Though such dsDNA molecules are probably not encapsulated, a general functional partition among the plasmids of each species resembles the L-and M-viruses of Saccharomyces cerevisiae. Invariably, there is a highly conserved autonomous element, which provides factors essential for cytoplasmic gene expression and replication (reviewed by Jeske et al 2006a;. Such element can exist solely or together with a non-autonomous element encoding a killer toxin.…”

Site-Directed Mutagenesis of the Heterotrimeric Killer Toxin Zymocin Identifies Residues Required for Early Steps in Toxin Action

“…k2 provides essential functions for cytoplasmic replication, transcription, and transcript processing, and several of these components show phylogenetic proximity to viruses (4,5). Since the proposed mode of replication via protein priming is typically found in viruses, the cytoplasmic linear dsDNA elements were termed virus-like elements (VLE) (6). The zymocin toxin is a heterotrimeric ␣␤␥ complex, the smallest subunit of which (␥) exhibits the cytotoxic ACNase activity (1,(7)(8)(9).…”