T ranscription i nitiation in eukaryotes requires many proteins: unlike bacteria, eukaryotes have three different polymerase each with different functions (see table, bacterial rna polymerase vs. eukaryotic rna polymerase i i: 1. while bacterial rna polymerase requires only a single additional protein ( factor) for transcription initiation to occur, eukaryotic rna polymerases require many additional proteins, collectively called the general transcription factors. Eukaryotic transcription initiation must deal with the packing of dna into nucleosomes and higher-order forms of chromatin structure, features absent from bacterial chromosomes. During transcription initiation, the serine located at the fifth position in the repeat sequence (ser5) is phosphorylated by. Tfiih: the polymerase can then disengage the factors, and begin transcription. Polymerase i i also requires activator, mediator, and chromatin. Second, eukaryotic transcription initiation requires the presence of a protein complex known as mediator, which allows the activator proteins to communicate properly with the polymerase i i and with the gtfs.