title: Length heterogeneity at conserved sequence block 2 in human mitochondrial DNA acts as a rheostat for RNA polymerase POLRMT activity.
abstract: The guanine (G)-tract of conserved sequence block 2 (CSB 2) in human mitochondrial DNA can result in transcription termination due to formation of a hybrid G-quadruplex between the nascent RNA and the nontemplate DNA strand. This structure can then influence genome replication, stability and localization. Here we surveyed the frequency of variation in sequence identity and length at CSB 2 amongst human mitochondrial genomes and used in vitro transcription to assess the effects of this length heterogeneity on the activity of the mitochondrial RNA polymerase, POLRMT. In general, increased G-tract length correlated with increased termination levels. However, variation in the population favoured CSB 2 sequences which produced efficient termination while particularly weak or strong signals were avoided. For all variants examined, the 3' end of the transcripts mapped to the same downstream sequences and were prevented from terminating by addition of the transcription factor TEFM. We propose that CSB 2 length heterogeneity allows variation in the efficiency of transcription termination without affecting the position of the products or the capacity for regulation by TEFM.
authors.affiliation: DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.
authors.forename: Benedict G
authors.initials: BG
authors.lastname: Tan
authors.affiliation: DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.
authors.forename: Frederick C
authors.initials: FC
authors.lastname: Wellesley
authors.affiliation: DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK n.j.savery@bristol.ac.uk.
authors.forename: Nigel J
authors.initials: NJ
authors.lastname: Savery
authors.affiliation: DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK mark.szczelkun@bristol.ac.uk.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Szczelkun
mesh_terms: D000225:Adenine / Q000378:metabolism; D001483:Base Sequence; D017124:Conserved Sequence / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics*; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D054856:G-Quadruplexes; D054629:Genome, Mitochondrial; D006801:Humans; D024101:Mitochondrial Proteins; D016366:Open Reading Frames / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D014157:Transcription Factors; D061806:Transcription Termination, Genetic
chemical_list: D004272:DNA, Mitochondrial; D024101:Mitochondrial Proteins; C560090:TEFM protein, human; D014157:Transcription Factors; D012321:DNA-Directed RNA Polymerases; C519567:POLRMT protein, human; D000225:Adenine