Two strand-specific origins of replication appear to be required for mammalian mitochondrial DNA (mtDNA) replication. Structural equivalents of these origins are found in the rep sequences of Saccharomyces cerevisiae mtDNA. These striking similarities have contributed to a universal model for the initiation of mtDNA replication in which a primer is created by cleavage of an origin region transcript. Consistent with this model are the properties of deletion mutants of yeast mtDNA ([rho-]) with a high density of reps (HS [rho-]). These mutant mtDNAs are preferentially inherited by the progeny resulting from the mating of HS [rho-] cells with cells containing wild-type mtDNA ([rho+]). This bias is presumed to result from a replication advantage conferred on HS [rho-] mtDNA by the high density of rep sequences acting as origins. To test whether transcription is indeed required for the preferential inheritance of HS [rho-] mtDNA, we deleted the nuclear gene (RPO41) for the mitochondrial RNA polymerase, reducing transcripts by at least 1000-fold. Since [rho-] genomes, but not [rho+] genomes, are stable when RPO41 is deleted, we examined matings between HS [rho-] and neutral [rho-] cells. Neutral [rho-] mtDNAs lack rep sequences and are not preferentially inherited in [rho-] x [rho+] crosses. In HS [rho-] x neutral [rho-] matings, the HS [rho-] mtDNA was preferentially inherited whether both parents were wild type or both were deleted for RPO41. Thus, transcription from the rep promoter does not appear to be necessary for biased inheritance. Our results, and analysis of the literature, suggest that priming by transcription is not a universal mechanism for mtDNA replication initiation.
展开▼
机译：哺乳动物的线粒体DNA（mtDNA）复制似乎需要两个特定于链的复制起点。这些来源的结构等价物在酿酒酵母mtDNA的rep序列中发现。这些惊人的相似性为启动mtDNA复制的通用模型做出了贡献，在该模型中，通过切割起源区域转录物创建了引物。与该模型一致的是具有高密度的代表（HSρ）的酵母mtDNA（ρ）的缺失突变体。这些突变型mtDNA优先由HS [rho-]细胞与含有野生型mtDNA（rho +）的细胞交配产生的后代继承。推测这种偏见是由于高密度的rep序列（作为起点）赋予HS mtDNA的复制优势所致。为了测试是否确实需要转录才能获得HS mtDNA的优先继承权，我们删除了线粒体RNA聚合酶的核基因（RPO41），将转录物减少了至少1000倍。由于删除RPO41时[rho-]基因组而不是[rho +]基因组是稳定的，因此我们检查了HS [rho-]和中性[rho-]细胞之间的交配。中性的mtDNA缺少rep序列，并且在交叉的[rho] x [rho +]中没有优先遗传。在HS r x中性rho交配中，无论是两个亲本都是野生型还是两个RPO41都被删除，HS mtDNA都是优先遗传的。因此，从rep启动子转录似乎不是有偏遗传的必要条件。我们的结果和文献分析表明，转录引发不是mtDNA复制起始的通用机制。
展开▼
