Final answer:
The cis-acting DNA sequence where the transcriptional initiation complex forms is the promoter, particularly the TATA box within it.
Step-by-step explanation:
The cis-acting DNA sequence at which the transcriptional initiation complex forms is called the promoter, specifically the TATA box within the promoter. The TATA box is the binding site for transcription factors and is located just upstream of the transcriptional start site. This box contains a consensus sequence, typically 5'-TATAAA-3', which is recognized by a protein complex called TFIID. The binding of TFIID to the TATA box allows for the recruitment of other transcription factors and stabilizes the preinitiation complex for the binding of RNA polymerase II, leading to the initiation of transcription.