what “RNA Polymerase” that makes the CO1 mRNA product on the electron

RNA polymerase is an essential enzyme that synthesizes RNA from a DNA template during the process of transcription. In the context of mitochondrial DNA (often referred to when discussing the cytochrome oxidase subunit 1, or CO1, gene), RNA polymerase is responsible for transcribing mitochondrial genes into mRNA, which can then be translated into proteins.

In electron microscopy, you might see RNA polymerase along with other transcriptional machinery at the site of active transcription. The CO1 gene, which encodes a subunit of cytochrome c oxidase, is important for mitochondrial function and energy production.

There are different types of RNA polymerases, but in eukaryotes (including human mitochondria), mitochondrial RNA polymerase (mtRNA polymerase) is specifically responsible for transcribing mitochondrial genes, including the CO1 gene. This enzyme recognizes specific promoter regions in the mitochondrial DNA and synthesizes a complementary RNA strand.

If you have a specific electron micrograph in mind, it might show the RNA polymerase in the act of transcribing the CO1 gene, along with other components of the transcriptional machinery such as transcription factors or nascent RNA strands.