Final answer:
In eukaryotes, the role of bacterial sigma factor is performed by RNA polymerase II, which assists in the transcription of messenger RNA along with distinct initiation proteins.
Step-by-step explanation:
The function of bacterial sigma factor in eukaryotes is performed by RNA polymerase II along with other transcription initiation proteins. Unlike in bacteria where a single RNA polymerase associates with one of several sigma factors to initiate transcription of different RNA types, eukaryotic cells utilize multiple RNA polymerases. Each RNA polymerase initiates transcription at a promoter sequence with the help of initiation proteins, including RNA polymerase II which is essential for messenger RNA (mRNA) transcription.
Sigma factors in bacteria are necessary to start the process of transcription by enabling the RNA polymerase to recognize specific promoter sequences of DNA. Eukaryotes, with a more complex cellular organization, lack operons that are characteristic of prokaryotic gene expression. Instead, eukaryotic genes have individual promoter sequences that are recognized by specific transcription factors and RNA polymerase II.