As the first step of gene expression, accurate transcription is essential to keep normal translation and the functions of proteins. Human mitochondrial RNA polymerase (POLRMT, for short), which exists in human mitochondria, is responsible for transcription of 13 subunits of the oxidative phosphorylation complexes, 2 ribosomal RNAs (rRNAs) and 22 transfer RNAs (tRNAs). POLRMT has the highest sequence similarity to bacteriophage T7 RNA polymerase, although it seems that the transcription elongation mechanism of POLRMT is much similar to that of nucleus RNA polymerase II (Pol II). In fact, there are also a few differences between the mitochondrial and the nucleus transcription elongations. First, distinct transcription elongation factors are present in mitochondria. For example, TE...[ Read more ]

As the first step of gene expression, accurate transcription is essential to keep normal translation and the functions of proteins. Human mitochondrial RNA polymerase (POLRMT, for short), which exists in human mitochondria, is responsible for transcription of 13 subunits of the oxidative phosphorylation complexes, 2 ribosomal RNAs (rRNAs) and 22 transfer RNAs (tRNAs). POLRMT has the highest sequence similarity to bacteriophage T7 RNA polymerase, although it seems that the transcription elongation mechanism of POLRMT is much similar to that of nucleus RNA polymerase II (Pol II). In fact, there are also a few differences between the mitochondrial and the nucleus transcription elongations. First, distinct transcription elongation factors are present in mitochondria. For example, TEFM (transcription elongation factor, mitochondria), which is a unique transcription factor in mitochondria can facilitate transcription elongation by interacting with POLRMT elongation complex. Second, mitochondrial DNA is more susceptible to DNA damages due to lack of nucleosome as well as of certain DNA repair mechanisms. Therefore, POLRMT has to go through damaged DNA more frequently. Here, we study the effects of DNA damages and transcription factors on mitochondrial transcription elongation. We found that POLRMT stalls at the Cisplatin and 8-oxoguanine DNA damage sites and some of these pauses/stalls can be enhanced by TFAM (transcription repression factor) and can be rescued by TEFM. We will expand these finding to understand the transcription elongation dynamics of POLRMT in the presence of DNA damages as well as mitochondrial transcription elongation factors by single-molecule and real-time machine--optical tweezers.

Key words: POLRMT, Transcription Elongation, Transcription Factors, Optical Tweezers, Dynamics