Transcripts of mitochondrial genes before they fully transform into mature mRNA , subject to few modifications posttranscriptional , which include splicing , editing and processing of three and 5 the end of the transcripts . Post-transcriptional processes leading to the formation of mature , functional mRNA is regulated by factors that stabilize or degrade these particles . The level of stable mitochondrial RNA is associated primarily with the transcriptional activity of the gene which is affected , inter alia, the construction of the promoter and the gene copy number .