[Alternative transcripts from POLRMT responsible for synthesis of nuclear RNA polymerase IV]

By analyzing ESTs that correspond to human POLRMT gene encoding mitochondrial RNA polymerase (mtRNAP) we revealed an alternatively spliced transcript. We confirmed the existence of the transcript that contain additional 225 nucleotides from proximal part of intron 1 by RT-PCR using RNA from HeLa cells. In mouse and rat there are similar alternative transcripts that contain entire intron 1 sequences. In addition, in mouse we revealed third transcript that contain extra exon derived from 142 bp of intron 2. The revealed alternative transcripts, in contrast to the mRNA encoding mtRNAP, specify N-terminally truncated protein lacking mitochondrial targeting signal. This protein has strictly nuclear localization and corresponds to nuclear RNA polymerase IV that we recently identified.