For example, recent studies suggested that one protein family, called the mitochondrial transcription termination factors, plays important roles in regulating the organellar transcription machinery. The mTERF proteins were first identified two decades ago as regulators of transcription termination in human mitochondria. Phylogenetic analyses of mTERF homologs in metazoans and plants revealed the presence of 4 subfamilies, mTERF1 to mTERF4. These proteins share a common 30-amino-acid repeat module called the mTERF motif. The proteins within this family possess diverse numbers and arrangements of these motifs, yet the folding patterns of these proteins are similar. Moreover, crystal structure studies of mTERF1, mTERF3 and mTERF4 suggest that the helical structure of the mTERF motifs may be essential for their nucleic acid-binding activities. Human mTERF1 binds specific sites located at the 39-end of the 16S rRNA and tRNALer genes to terminate mitochondrial transcription. Additionally, mTERF1 binds to the mitochondrial transcription initiation site to create a DNA loop that allows for the recycling of the transcriptional machinery. This simultaneous link between mitochondrial transcriptional initiation and termination sites may explain the high rate of mitochondrial rRNA biogenesis. mTERF2 binds to mitochondrial DNA in a non-specific manner and associates with nucleoids. mTERF2 loss-of-function mice exhibit myopathies, memory deficits, and impaired respiratory function due to a reduction in the number of mitochondrial transcripts. mTERF3 is essential, and mTERF3-knockout mice die during the early stages of embryogenesis; mTERF3 non-specifically interacts with mtDNA promoter regions and mediates the repression of mitochondrial transcription initiation. Mouse NSUN4 is a methyltransferase involved in the methylation of ribosomes. Mouse mTERF4 first binds 16S and 12S rRNAs, then forms a stoichiometric complex with NSUN4, which is essential for proper mitochondrial ribosomal LDK378 1032900-25-6 assembly and translation. Our genetic, molecular and biochemical results indicate that mTERF15 is a unique, mitochondria-localized protein with RNA-binding activity. This protein is critical for post-transcriptional modification in the RNA splicing of mitochondrial nad2 intron 3. Mutating mTERF15 impaired the normal activity of mitochondrial respiratory chain complex I, thereby resulting in abnormal mitochondrial development and the widespread retardation of plant growth and development. mTERFs constitute a broad family of eukaryotic proteins that are essential for the initiation and termination of organellar transcription and the translation and replication of the organellar transcription machinery ; however, mounting evidence suggests an emerging role for these proteins in RNA splicing in plants. The human genome contains only 4 genes encoding mTERF paralogs, whereas the Arabidopsis genome contains at least 35 genes for mTERF proteins with a diverse arrangement and number of mTERF motifs.