GRE Subject Test: Biochemistry, Cell, and Molecular Biology › Help with Gene Regulation Proteins
Histone acetyltransferases (HATs) transfer acetyl groups from acetyl CoA to lysine residues on histones. What is the purpose of this transfer?
Promote formation of euchromatin and increase gene expression
Facilitate phosphorylation of these lysines by kinases
Signal for ubiquitin-mediated degredation of histones
Prevent transcription factors from binding to DNA
Prevent DNA degredation by endonucleases
The correct answer is to promote formation of euchromatin and increase gene expression. Acetylation of histones "relaxes" DNA coiling around histones by reducing the affinity between histones and DNA. This allows transcription factors to bind promoter regions and promote increased gene expression via transcription.
NFkB is a transcription factor that is held inactive in the cytoplasm when bound by its inhibitor, IkB. Upstream signaling that activates NFkB causes what effect?
Ubiquitin-mediated degradation of IkB, allowing NFkB to translocate to the nucleus and initiate transcription
Ubiquitin-mediated degradation of NFkB
Ubiquitin-mediated degradation of IkB, causing a conformational shift in NFkB that renders its DNA-binding domain inaccessible
Recruitment of transcription factors and coactivators of transcription to the cytoplasmically sequestered NFkB
Ubiquitin-mediated degradation of NFkB, allowing IkB to translocate to the nucleus and initiate transcription
Upstream signaling, such as from a toll-like receptor, causes IKK to phosphorylate IkB, signaling for its ubiquitin-mediated degradation. Since NFkB is no longer bound by its inhibitor, IkB, it translocates to the nucleus where it binds specific motifs in the genome to recruit other transcriptional machinery and initiate transcription.
What is the role of mediator in gene expression?
Mediator is a coactivator of transcription and serves to recruit transcription factors and RNA polymerase II
Mediator suppresses transcription by methylating histone lysines
Mediator is not involved in gene expression
Mediator is a thermostable DNA polymerase that replicates DNA in extreme temperatures
Mediator facilitates alternative splicing of newly synthesized mRNA transcripts
The correct answer is that mediator is a coactivator of transcription and serves to recruit transcription factors and RNA polymerase II. Mediator does not directly initiate transcription; however, by protein-protein interactions, it recruits the necessary proteins to sites of transcription.
Which of the following is not a way in which transcription factors influence gene-specific transcription?
Recruiting DNA polymerase
Recruiting RNA polymerase holoenzyme
Recruiting other transcription factors
Binding transcription factor-specific DNA motifs
Promoting euchromatin formation
The correct answer is recruiting DNA polymerase. DNA polymerase is involved in DNA replication, not transcription. Pioneer transcription factors can bind specific DNA motifs and promote euchromatin formation, allowing other transcription factors to bind the less organized DNA. Transcription factors can recruit other transcription factors and the RNA polymerase holoenzyme to promoters to promote gene-specific transcription.