Hermanns J, Osiewacz H D
Deutsches Krebsforschungszentrum, Forschungsschwerpunkt: Angewandte Tumorvirologie, Abteilung: Molekularbiologie der Alterungsprozesse, Heidelberg, Federal Republic of Germany.
Curr Genet. 1992 Dec;22(6):491-500. doi: 10.1007/BF00326415.
The molecular characterization of an additional DNA species (pAL2-1) which was identified previously in a long-lived extrachromosomal mutant (AL2) of Podospora anserina revealed that this element is a mitochondrial linear plasmid. pAL2-1 is absent from the corresponding wild-type strain, has a size of 8395 bp and contains perfect long terminal inverted repeats (TIRs) of 975 bp. Exonuclease digestion experiments indicated that proteins are covalently bound at the 5' termini of the plasmid. Two long, non-overlapping open reading frames, ORF1 (3,594 bp) and ORF2 (2847 bp), have been identified, which are located on opposite strands and potentially encode a DNA and an RNA polymerase, respectively. The ORF1-encoded polypeptide contains three conserved regions which may be responsible for a 3'-5' exonuclease activity and the typical consensus sequences for DNA polymerases of the D type. In addition, an amino-acid sequence motif (YSRLRT), recently shown to be conserved in terminal proteins from various bacteriophages, has been identified in the amino-terminal part of the putative protein. According to these properties, this first linear plasmid identified in P. anserina shares all characteristics with invertrons, a group of linear mobile genetic elements.
先前在嗜热栖热放线菌的一个长寿的染色体外突变体（AL2）中鉴定出的另一种DNA物种（pAL2-1）的分子特征表明，该元件是一种线粒体线性质粒。相应的野生型菌株中不存在pAL2-1，其大小为8395 bp，包含975 bp的完美长末端反向重复序列（TIR）。核酸外切酶消化实验表明，蛋白质与质粒的5'末端共价结合。已鉴定出两个长的、不重叠的开放阅读框，ORF1（3594 bp）和ORF2（2847 bp），它们位于相反的链上，可能分别编码一种DNA聚合酶和一种RNA聚合酶。ORF1编码的多肽包含三个保守区域，可能负责3'-5'核酸外切酶活性以及D型DNA聚合酶的典型共有序列。此外，在假定蛋白质的氨基末端部分鉴定出一个氨基酸序列基序（YSRLRT），最近已证明该基序在各种噬菌体的末端蛋白质中是保守的。根据这些特性，在嗜热栖热放线菌中鉴定出的第一个线性质粒与反转子（一组线性移动遗传元件）具有所有共同特征。
