Tracy R L, Stern D B
Boyce Thompson Institute for Plant Research, Cornell University, Ithaca, NY 14853, USA.
Curr Genet. 1995 Aug;28(3):205-16. doi: 10.1007/BF00309779.
A diversity of promoter structures. It is evident that tremendous diversity exists between the modes of mitochondrial transcription initiation in the different eukaryotic kingdoms, at least in terms of promoter structures. Within vertebrates, a single promoter for each strand exists, which may be unidirectional or bidirectional. In fungi and plants, multiple promoters are found, and in each case, both the extent and the primary sequences of promoters are distinct. Promoter multiplicity in fungi, plants and trypanosomes reflects the larger genome size and scattering of genes relative to animals. However, the dual roles of certain promoters in transcription and replication, at least in yeast, raises the interesting question of how the relative amounts of RNA versus DNA synthesis are regulated, possibly via cis-elements downstream from the promoters. Mitochondrial RNA polymerases. With respect to mitochondrial RNA polymerases, characterization of human, mouse, Xenopus and yeast enzymes suggests a marked degree of conservation in their behavior and protein composition. In general, these systems consist of a relatively non-selective core enzyme, which itself is unable to recognize promoters, and at least one dissociable specificity factor, which confers selectivity to the core subunit. In most of these systems, components of the RNA polymerase have been shown to induce a conformational change in their respective promoters and have also been assigned the role of a primase in the replication of mtDNA. While studies of the yeast RNA polymerase have suggested it has both eubacterial (mtTFB) and bacteriophage (RPO41) origins, it is not yet clear whether these characteristics will be conserved in the mitochondrial RNA polymerases of all eukaryotes. mtTFA-mtTFB; conserved but dissimilar functions. With respect to transcription factors, mtTFA has been found in both vertebrates and yeast, and may be a ubiquitous protein in mitochondria. However, the divergence in non-HMG portions of the proteins, combined with differences in promoter structure, has apparently relegated mtTFA to alternative, or at least non-identical, physiological roles in vertebrates and fungi. The relative ease with which mtTFA can be purified (Fisher et al. 1991) suggests that, where present, it should be facile to detect. mtTFB may represent a eubacterial sigma factor adapted for interaction with the mitochondrial RNA polymerase.(ABSTRACT TRUNCATED AT 400 WORDS)
启动子结构的多样性。很明显，不同真核生物界中线粒体转录起始模式之间存在巨大差异，至少在启动子结构方面是这样。在脊椎动物中，每条链有一个单一的启动子，它可以是单向的或双向的。在真菌和植物中，发现了多个启动子，并且在每种情况下，启动子的范围和一级序列都是不同的。真菌、植物和锥虫中的启动子多样性反映了相对于动物而言更大的基因组大小和基因的分散性。然而，某些启动子在转录和复制中的双重作用，至少在酵母中是这样，这就提出了一个有趣的问题，即RNA与DNA合成的相对量是如何调控的，可能是通过启动子下游的顺式元件。线粒体RNA聚合酶。关于线粒体RNA聚合酶，对人类、小鼠、非洲爪蟾和酵母酶的表征表明它们在行为和蛋白质组成上有显著程度的保守性。一般来说，这些系统由一个相对非选择性的核心酶组成，其本身无法识别启动子，以及至少一个可解离的特异性因子，该因子赋予核心亚基选择性。在这些系统中的大多数中，RNA聚合酶的组分已被证明能在其各自的启动子中诱导构象变化，并且在mtDNA复制中也被赋予了引发酶的作用。虽然对酵母RNA聚合酶的研究表明它具有真细菌（mtTFB）和噬菌体（RPO41）的起源，但尚不清楚这些特征是否会在所有真核生物的线粒体RNA聚合酶中保守。mtTFA - mtTFB；功能保守但不同。关于转录因子，在脊椎动物和酵母中都发现了mtTFA，并且它可能是线粒体中一种普遍存在的蛋白质。然而，蛋白质非HMG部分的差异，加上启动子结构的不同，显然使mtTFA在脊椎动物和真菌中承担了不同的，或者至少是不相同的生理作用。mtTFA相对容易纯化（Fisher等人，1991年）表明，在存在的情况下，应该很容易检测到。mtTFB可能代表一种适应于与线粒体RNA聚合酶相互作用 的真细菌σ因子。（摘要截选至400字）
