Breitenberger C A, Browning K S, Alzner-DeWeerd B, RajBhandary U L
EMBO J. 1985 Jan;4(1):185-95. doi: 10.1002/j.1460-2075.1985.tb02335.x.
We have used RNA gel transfer hybridization, S1 nuclease mapping and primer extension to analyze transcripts derived from several genes in Neurospora crassa mitochondria. The transcripts studied include those for cytochrome oxidase subunit III, 17S rRNA and an unidentified open reading frame. In all three cases, initial transcripts are long, include tRNA sequences, and are subsequently processed to generate the mature RNAs. We find that endpoints of the most abundant transcripts generally coincide with those of tRNA sequences. We therefore conclude that tRNA sequences in long transcripts act as primary signals for RNA processing in N. crassa mitochondria. The situation is somewhat analogous to that observed in mammalian mitochondrial systems. The difference, however, is that in mammalian mitochondria, noncoding spacers between tRNA, rRNA and protein genes are very short and in many cases non-existent, allowing no room for intergenic RNA processing signals whereas, in N. crassa mtDNA, intergenic non-coding sequences are usually several hundred nucleotides long and contain highly conserved GC-rich palindromic sequences. Since these GC-rich palindromic sequences are retained in the processed mature RNAs, we conclude that they do not serve as signals for RNA processing.
我们运用RNA凝胶转移杂交、S1核酸酶图谱分析和引物延伸技术，来分析粗糙脉孢菌线粒体中多个基因产生的转录本。所研究的转录本包括细胞色素氧化酶亚基III、17S rRNA以及一个未鉴定的开放阅读框的转录本。在所有这三种情况下，初始转录本都很长，包含tRNA序列，随后经过加工生成成熟RNA。我们发现，最丰富的转录本的末端通常与tRNA序列的末端一致。因此我们得出结论，长转录本中的tRNA序列充当粗糙脉孢菌线粒体中RNA加工的主要信号。这种情况与在哺乳动物线粒体系统中观察到的情况有些类似。然而，不同之处在于，在哺乳动物线粒体中，tRNA、rRNA和蛋白质基因之间的非编码间隔非常短，在许多情况下甚至不存在，没有基因间RNA加工信号的空间，而在粗糙脉孢菌线粒体DNA中，基因间非编码序列通常有几百个核苷酸长，并且包含高度保守的富含GC的回文序列。由于这些富含GC的回文序列保留在加工后的成熟RNA中，我们得出结论，它们不作为RNA加工的信号。
