Stamper S E, Dewey R E, Bland M M, Levings C S
Department of Genetics, North Carolina State University, Raleigh 27695-7614.
Curr Genet. 1987;12(6):457-63. doi: 10.1007/BF00434824.
We have previously identified two large open reading frames, designated ORF13 and ORF25, in the Texas male-sterile cytoplasm (cms-T) of maize mitochondrial DNA (mtDNA). ORF13 is a single copy gene of chimeric origin that is uniquely transcribed and translated in the mitochondria of cms-T maize, where it produces a polypeptide of approximately 13,000 Mr. The ORF13 reading frame does not occur in the maize N, C or S cytoplasms or Nicotiana tabacum. ORF25 exists as a single copy and is transcribed in the four major maize cytoplasms (N, T, C and S) and N. tabacum. The predicted ORF25 polypeptide has a molecular weight of 24,374 in normal maize and 22,439 in tobacco. Several nucleotide and predicted amino acid changes have occurred in the ORF25 gene among the four maize cytoplasms and N. tabacum. Properties such as transcription and conservation of the sequence between two diverse species suggests that ORF25 encodes a functional plant mitochondrial gene. The ORF25 sequence of maize contains a chloroplast DNA insert homologous to a tRNA-Arg gene; this chloroplast DNA insert is absent in the tobacco ORF25 sequence. Comparison of the ORF25 and ORF13 sequences in restored and non-restored cms-T indicates no differences in their nucleotide sequences. Thus fertility restoration does not alter the primary sequences of ORF13 or ORF25.
我们之前在玉米线粒体DNA（mtDNA）的德克萨斯雄性不育细胞质（cms-T）中鉴定出两个大的开放阅读框，分别命名为ORF13和ORF25。ORF13是一个嵌合起源的单拷贝基因，仅在cms-T玉米的线粒体中进行转录和翻译，在那里它产生一种分子量约为13,000的多肽。ORF13阅读框在玉米N、C或S细胞质以及烟草中均未出现。ORF25以单拷贝形式存在，在玉米的四种主要细胞质（N、T、C和S）以及烟草中均有转录。预测的ORF25多肽在正常玉米中的分子量为24,374，在烟草中的分子量为22,439。在四种玉米细胞质和烟草之间，ORF25基因发生了一些核苷酸和预测氨基酸的变化。转录以及两个不同物种之间序列保守性等特性表明ORF25编码一个功能性的植物线粒体基因。玉米的ORF25序列包含一个与tRNA-Arg基因同源的叶绿体DNA插入片段；烟草的ORF25序列中不存在这个叶绿体DNA插入片段。对恢复育性和未恢复育性的cms-T中的ORF25和ORF13序列进行比较，结果表明它们的核苷酸序列没有差异。因此，育性恢复并没有改变ORF13或ORF25的一级序列。
