Revision of the nucleotide sequence and RNA splicing pathway of the Neurospora mitochondrial gene encoding ATPase subunit 6.

Previous sequence analysis of the Neurospora oli2 (ATP6) mitochondrial gene suggested that, in addition to a typical Group-I intron, it contained an unusual, mostly-palindromic, 93-nucleotide intron. We report here revisions of the nucleotide sequence and analysis of the size and sequence of reverse-transcriptase PCR products that show: (1) the Group-I intron splice sites are located as predicted by previous DNA sequence analysis; (2) the putative 93-nt intron is not excised from the mature mRNA, and most of this sequence is actually in the 5' untranslated region. We conclude that the Neurospora ATP6 gene contains only one intron. Analysis of the cDNA sequence also confirms the non-universal nature of the Neurospora mitochondrial genetic code: a TGA codon inferred from the DNA sequence is present as UGA in the mRNA. This provides direct evidence that this codon is not altered, for example by RNA editing, to conform to the universal code.