Actual site of transcription in eukaryotes is
Transcription takes place inside the nucleus of eukaryotes, where DNA will be read to synthesise RNA molecules from it, whil will then move out of the nucleus. RNA molecules go to ribosomes in the cytoplasm where translation (protein synthesis) occurs.
Mesosomes are the invaginations of the plasma membrane of prokaryotes.
Ribosomes present in the cytoplasm along with RNA help in the formation of protein via translation process thus they are called protein factories of the cells.