Termination of transcription in human mitochondria: identification and purification of a DNA binding protein factor that promotes termination.

In a transcription system using a HeLa cell mitochondrial lysate programmed by mitochondrial DNA constructs containing the main heavy strand promoter and the transcription termination site at the 16S rRNA/leucyl-tRNA boundary, an appreciable fraction of the heavy strand transcripts terminates at this site, as it does in vivo. A DNA binding protein(s) that protects a 28 bp region immediately adjacent and downstream of the 3' ends of the in vivo and in vitro transcripts has been identified in the lysate and highly purified on an oligodeoxynucleotide affinity column. An activity promoting specific termination of heavy strand transcripts copurified with the DNA binding protein(s), pointing to the involvement of this protein in transcription termination. A distinctive modification of the footprint not correlated with terminating activity has also been observed.