Gene expression is a biological process where information in genes creates functional products, like proteins. This process allows cells to perform diverse functions, grow, and respond to their environment. Proteins are molecular machines that carry out specific tasks in gene expression. Among these, Transcription Factor II B (TFIIB) is a significant contributor.
Defining TFIIB
Transcription Factor II B (TFIIB) is a general transcription factor, universally required for the accurate initiation of transcription by RNA polymerase II. RNA polymerase II synthesizes messenger RNA (mRNA) from DNA templates, a crucial step in gene expression. TFIIB is a single polypeptide chain, around 30-35 kilodaltons, and a component of the basal transcription machinery. Its structure includes distinct domains, like a C-terminal core and an N-terminal zinc ribbon, involved in protein-protein and protein-DNA interactions.
TFIIB’s Central Role in Gene Expression
TFIIB is central to the initial stages of gene expression, particularly during the formation of the preinitiation complex (PIC) at gene promoters. This complex is a large assembly of proteins that positions RNA polymerase II to begin transcribing a gene. TFIIB acts as a molecular bridge, connecting the TATA-binding protein (TBP), which recognizes the TATA box, with RNA polymerase II. This ensures transcription initiation occurs at the correct start site on the DNA template.
How TFIIB Orchestrates Transcription
TFIIB’s orchestration of transcription begins with its interaction with TBP, which is bound to the TATA box within the gene promoter. TFIIB binds to both TBP and the DNA, wrapping around it in a specific orientation. This binding creates a scaffold, facilitating the recruitment of RNA polymerase II and other general transcription factors (TFIIF, TFIIE, TFIIH) to form the complete preinitiation complex. TFIIB also directly positions RNA polymerase II precisely over the transcription start site; its N-terminal domain extends into the polymerase’s active site, orienting the enzyme for accurate RNA synthesis. Finally, TFIIB contributes to promoter melting, unwinding the DNA double helix to create a single-stranded template accessible for transcription.
The Broader Impact of TFIIB
The precise function of TFIIB is significant for accurate and regulated gene expression, which underpins all cellular processes. Proper gene functioning, from cell growth to metabolism, relies on the accurate initiation provided by factors like TFIIB. Its role in assembling the core transcriptional machinery ensures genes are turned on and off at the right time and place. Any errors or dysfunctions in TFIIB activity can have widespread consequences for cellular health and organismal development. This highlights its important contribution to maintaining cellular homeostasis.
References
url: “https://vertexaisearch.googleapis.com/v1/projects/103923951751/locations/global/collections/default_collection/dataStores/default_data_store/servingConfigs/default_serving_config:search?query=TFIIB+function”, title: “TFIIB function”
url: “https://vertexaisearch.googleapis.com/v1/projects/103923951751/locations/global/collections/default_collection/dataStores/default_data_store/servingConfigs/default_serving_config:search?query=TFIIB+molecular+structure”, title: “TFIIB molecular structure”
url: “https://vertexaisearch.googleapis.com/v1/projects/103923951751/locations/global/collections/default_collection/dataStores/default_data_store/servingConfigs/default_serving_config:search?query=TFIIB+preinitiation+complex+assembly+RNA+polymerase+II”, title: “TFIIB preinitiation complex assembly RNA polymerase II”