Regulation of mitochondrial transcription by mitochondrial transcription factor A (original) (raw)
Related papers
Nucleic Acids Research, 2003
Mitochondrial transcription factor A (TFAM) has been shown to stimulate transcription from mitochondrial DNA promoters in vitro. In order to determine whether changes in TFAM levels also regulate RNA synthesis in situ, recombinant human precursor proteins were imported into the matrix of rat liver mitochondria. After uptake of wt-TFAM, incorporation of [a-32 P]UTP into mitochondrial mRNAs as well as rRNAs was increased 2-fold (P < 0.05), whereas import of truncated TFAM lacking 25 amino acids at the C-terminus had no effect. Import of wt-TFAM into liver mitochondria from hypothyroid rats stimulated RNA synthesis up to 4-fold. We conclude that the rate of transcription is submaximal in freshly isolated rat liver mitochondria and that increasing intra-mitochondrial TFAM levels is suf®cient for stimulation. The low transcription rate associated with the hypothyroid state observed in vivo as well as in organello seems to be a result of low TFAM levels, which can be recovered by treating animals with T3 in vivo or by importing TFAM in organello. Thus, this protein meets the criteria for being a key factor in regulating mitochondrial gene expression in vivo.
Human mitochondrial transcription factor A possesses multiple subcellular targeting signals
FEBS Journal, 2007
Mitochondrial transcription factor A (TFAM, mtTFA) is a member of a high-mobility group (HMG) of proteins named on the basis of their electrophoretic mobility in polyacrylamide gels. This group is composed of nonhistone chromatin proteins and transcription factors that can bind DNA either nonspecifically or in a sequence-dependent manner [1]. TFAM is encoded in the nucleus and is synthesized on cytoplasmic ribosomes as a precursor, which is converted, upon mitochondrial importation, into a 24.4 kDa, 204 amino acid mature form. The N-terminal sequence of the precursor has not been determined, and therefore it is possible that translation can start on either of two N-terminal methionines, resulting in either 246 amino acid (29 kDa) or 240 amino acid (28.4 kDa) precursors . The mature form contains two HMG boxes, Abbreviations EGFP, enhanced green fluorescent protein; HMG, high-mobility group; HMG1 and HMG2, HMG-like domains of human mitochondrial transcription factor A; hTFAM, human mitochondrial transcription factor A; MTS, mitochondrial targeting sequence; NLS, nuclear localization sequence; N ⁄ C, nucleus-to-cytoplasm; SOD2, manganese superoxide dismutase; Tc, tetracycline; TFAM, mitochondrial transcription factor A.
The Italian journal of biochemistry, 2007
The mitochondrial transcription factor A (Tfam) is a mitochondrial protein encoded in the nucleus. The gene for Tfam spans about 10 kb and consists of seven exons and six introns. In human and rat, exon 5 can splite alternatively resulting in two Tfam isoforms. In order to investigate the role of the delta 5Tfam isoform in human cells, we studied its stability in vitro, then we carried out overexpression experiments in H1299 human cell line in order to clarify the in vivo effect of this shorter isoform of Tfam. The data obtained by Real time-PCR demonstrate that the overexpression of delta 5Tfam causes an increase of mitochondrial transcription, so also this isoform as a role in the mitochondrial process.
Mammalian transcription factor A is a core component of the mitochondrial transcription machinery
Proceedings of the National Academy of Sciences of the United States of America, 2012
Transcription factor A (TFAM) functions as a DNA packaging factor in mammalian mitochondria. TFAM also binds sequence-specifically to sites immediately upstream of mitochondrial promoters, but there are conflicting data regarding its role as a core component of the mitochondrial transcription machinery. We here demonstrate that TFAM is required for transcription in mitochondrial extracts as well as in a reconstituted in vitro transcription system. The absolute requirement of TFAM can be relaxed by conditions that allow DNA breathing, i.e., low salt concentrations or negatively supercoiled DNA templates. The situation is thus very similar to that described in nuclear RNA polymerase II-dependent transcription, in which the free energy of supercoiling can circumvent the need for a subset of basal transcription factors at specific promoters. In agreement with these observations, we demonstrate that TFAM has the capacity to induce negative supercoils in DNA, and, using the recently developed nucleobase analog FRET-pair tC O -tC nitro , we find that TFAM distorts significantly the DNA structure. Our findings differ from recent observations reporting that TFAM is not a core component of the mitochondrial transcription machinery. Instead, our findings support a model in which TFAM is absolutely required to recruit the transcription machinery during initiation of transcription.
Gene, 2002
Mitochondrial transcription factor A (mtTFA or Tfam) is a 25 kDa protein encoded by a nuclear gene and imported to mitochondria, where it functions as a key regulator of mammalian mitochondrial (mt) DNA transcription and replication. The coding sequence of the human mtTFA gene is reported in the literature and the sizes of few introns are known. In this paper we present the genomic structure of the human mtTFA gene along with the complete sequence of its six intronic regions. Three of the introns (I, III, VI) have been found to be less than 600 bp, while the other three were greater than 1.8 kb. In the course of this work, we discovered that, in addition to the active copy, different homologous sequences identified as processed pseudogenes ch-mtTFA have been isolated and sequenced. Using an 'in silico' mapping approach we determined their locations on chromosomes 7, 11 and X. ch-mtTFA locations are different from that of the gene, previously reported on chromosome 10. Transcription analysis by means of reverse transcriptase-polymerase chain reaction has shown that other than the RNA corresponding to the full-length transcript, an isoform lacking 96 bp is also present. Among the three sequenced pseudogenes only one of them located on chromosome 11 has been found to be transcribed in Jurkat cells under these culture conditions, even though transcription initiation and binding sites for different transcription factors have also been found upstream from the other two pseudogenes. q
Mitochondrial transcription: Lessons from mouse models
Biochimica et Biophysica Acta (BBA) - Gene Regulatory Mechanisms, 2012
Mammalian mitochondrial DNA (mtDNA) is a circular double-stranded DNA genome of~16.5 kilobase pairs (kb) that encodes 13 catalytic proteins of the ATP-producing oxidative phosphorylation system (OXPHOS), and the rRNAs and tRNAs required for the translation of the mtDNA transcripts. All the components needed for transcription and replication of the mtDNA are, therefore, encoded in the nuclear genome, as are the remaining components of the OXPHOS system and the mitochondrial translation machinery. Regulation of mtDNA gene expression is very important for modulating the OXPHOS capacity in response to metabolic requirements and in pathological processes. The combination of in vitro and in vivo studies has allowed the identification of the core machinery required for basal mtDNA transcription in mammals and a few proteins that regulate mtDNA transcription. Specifically, the generation of knockout mouse strains in the last several years, has been key to understanding the basis of mtDNA transcription in vivo. However, it is well accepted that many components of the transcription machinery are still unknown and little is known about mtDNA gene expression regulation under different metabolic requirements or disease processes. In this review we will focus on how the creation of knockout mouse models and the study of their phenotypes have contributed to the understanding of mitochondrial transcription in mammals. This article is part of a Special Issue entitled: Mitochondrial Gene Expression.
Mitochondrial transcription in mammalian cells
Frontiers in Bioscience, 2017
As a consequence of recent discoveries of intimate involvement of mitochondria with key cellular processes, there has been a resurgence of interest in all aspects of mitochondrial biology, including the intricate mechanisms of mitochondrial DNA maintenance and expression. Despite four decades of research, there remains a lot to be learned about the processes that enable transcription of genetic information from mitochondrial DNA to RNA, as well as their regulation. These processes are vitally important, as evidenced by the lethality of inactivating the central components of mitochondrial transcription machinery. Here, we review the current understanding of mitochondrial transcription and its regulation in mammalian cells. We also discuss key theories in the field and highlight controversial subjects and future directions as we see them.
Biochimie, 1999
Mitochondrial function requires genes encoded in both mitochondrial and nuclear genomes. Tfam, the activator of mammalian mitochondrial transcription, is encoded in the nucleus and its expression has been shown in in vitro studies to be controlled by nuclear respiratory factors NRF-1 and NRF-2. In order to understand the physiological dependence of mitochondrial gene expression, we have analyzed in rat liver, testis and brain the expression level of mitochondrial genes in parallel with those of the three transcription factors. We found that: a) Tfam expression is down-regulated in rat testis, both at the protein and transcript level. The three-fold reduction in the abundance of Tfam protein in rat testis does not result in low steady-state levels of mitochondrial gene transcripts, suggesting that Tfam is in excess and does not limit transcription in vivo; and b) NRF-1 and NRF-2 (α, and γ subunits) mRNAs were analyzed by Northern blotting; for each mRNA, several transcripts were observed as well as tissue-specific patterns of expression. The mRNA steady-state levels of NRF-1 and NRF-2 were higher in testis than in liver or brain. These data suggest that the low expression level of Tfam found in testis is not due to decreased NRF-1 and/or NRF-2 expression and further suggest the existence of tissue-specific post-transcriptional regulatory mechanisms for the expression of NRF-1/NRF-2 genes. © 1999 Société française de biochimie et biologie moléculaire / Éditions scientifiques et médicales Elsevier SAS mitochondrial gene expression / mitochondrial transcription factor A / nuclear respiratory factors 1 and 2 / messenger and protein steady-state levels / rat tissues * Present address: Laboratoire de Biologie Moleculaire et Cellulaire, CNRS-UMR 49, École Normale Superieure de Lyon, 46, allee d'Italie, 69364 Lyon cedex 07, France ** Correspondence and reprints Abbreviations: Tfam, mitochondrial transcription factor A; NRF-1, nuclear respiratory factor 1; NRF-2, nuclear respiratory factor 2.
Mitochondrial protein expression in rat and in human cells
2000
I nthe present paper, we analyzed some aspects of the post-transcriptional regulation of two COX (cy- tochrome c oxidase) subunits, i.e. mitochondrion-encoded COXIII and nucleus-encoded COXIV. In particular, by T1 RNase protection assays, we found two proteins, present in mitochondrial extracts from adult rat brain and testis, able to bind COXIII mRNA. We also found cytoplasmic proteins present in testis,