DmTTF, a novel mitochondrial transcription termination factor that recognises two sequences of Drosophila melanogaster mitochondrial DNA

Abstract

Using a combination of bioinformatic and molecular biology approaches a Drosophila melanogaster protein, DmTTF, has been identified, which exhibits sequence and structural similarity with two mitochondrial transcription termination factors, mTERF (human) and mtDBP (sea urchin). Import/processing assays indicate that DmTTF is synthesised as a precursor of 410 amino acids and is imported into mitochondria, giving rise to a mature product of 366 residues. Band-shift and DNase I protection experiments show that DmTTF binds two homologous, short, non-coding sequences of Drosophila mitochondrial DNA, located at the 3' end of blocks of genes transcribed on opposite strands. The location of the target sequences coincides with that of two of the putative transcription termination sites previously hypothesised. These results indicate that DmTTF is the termination factor of mitochondrial transcription in Drosophila. The existence of two DmTTF binding sites might serve not only to stop transcription but also to control the overlapping of a large number of transcripts generated by the peculiar transcription mechanism operating in this organism.

Drosophila Mitochondrial Transcription Factor B2 Regulates Mitochondrial DNA Copy Number and Transcription in Schneider Cells

“…Although information on transcriptional mechanism in Drosophila remains limited, several polycistronic transcripts were identified and mapped by Berthier et al (42), suggesting that Drosophila mtDNA is transcribed polycistronically as in other organisms, and similar to mammals, mitochondrial rRNAs were found to be more abundant than mRNAs (42). Recently, Drosophila mitochondrial transcription termination factor was identified that mediates termination of transcription of the ribosomal unit, accounting for the excess production of mitochondrial rRNAs (43). Overall, we found that mRNA levels were reduced more than the levels of mtDNA, and this, too, may reflect a higher turnover rate for mRNAs as compared with that of mtDNA.…”

Mitochondrial COI-NC-COII sequences in talitrid amphipods (Crustacea)

“…Such NC regions also show high AT-bias, high length variability and are able to form stem-loop structures as observed even in regions close to COI, COII or tRNALeu(UUR) genes (Smith and Bush, 1997;De La Rua et al, 2000;Shao et al, 2001;Soucy and Danforth, 2002;Dowton et al, 2003;Yamauchi et al, 2003). They might have a role in transcription in addition to that of the mt control region (see Valverde et al, 1994b;Roberti et al, 2003). Moreover, secondary structure of the NC regions could play a similar role to that of tRNA genes in the processing of mt transcripts (Valverde et al, 1994a;Garesse et al, 1997).…”

Mitochondrial Genomes Provide Insights into the Phylogeny of Lauxanioidea (Diptera: Cyclorrhapha)

“…In the present study, a conserved 15 bp region was confirmed as present in all 79 available cyclorrhaphan mt genomes. More research is needed to determine the functions of conserved non-coding region in insect genomes, although the ND1-tRNA Ser(UCN) spacer has been proposed as a likely translation termination site mtTERM, that controls over-expression of the rRNA genes relative to the protein-coding genes [57,58]. …”