What is the primary role of the TATA-binding protein (TBP)?

The TATA-binding protein (TBP) plays a crucial role in the initiation of transcription in eukaryotic cells by binding specifically to the TATA box, a conserved DNA sequence located in the promoter region of many genes. This binding is a critical step in the formation of the transcription initiation complex. Once TBP attaches to the TATA box, it causes the DNA to bend, which facilitates the recruitment of other transcription factors and RNA polymerase to the promoter. This assembly of proteins is essential for the start of transcription, as it effectively positions RNA polymerase at the transcription start site, allowing it to begin synthesizing RNA from the DNA template.

The other roles mentioned, such as diffusing mRNA into the nucleus, synthesizing ribosomal RNA, or modifying RNA transcripts post-transcription, are not associated with TBP. Instead, these tasks are carried out by different proteins and processes within the cell. Thus, the primary function of TBP in binding to the TATA box to initiate transcription is fundamental to gene expression regulation in eukaryotes.