Transcriptional control of development by homeobox genes

Transcriptional control of development by homeobox genes (Ultrabithorax (Ubx))

Tissue specific transcriptional control experimentally demonstrated by nascent-chain (run-on) analysis:

Construction of a 5' deletion series to locate transcriptional control regions in a eukaryotic gene.

Transcription Elements:
    3 Types:
        Promoter, Promoter-Proximal, Enhancer

Experimental elucidation of Promoter-Proximal Elements through linkage scanning mutational analyses: (hatched regions have scrambled sequences)

Linkage scanning analysis of the herpes simplex virus (HSV) thymidine kinase (tk) control region

PE-1 and PE-2 are promoter-proximal elements, TATA box is promoter element (for actual sequences of these elements, see diagram of tk above)

General pattern of transcriptional regulation complexity in a eukaryotic gene from mammals and yeast.

Transcriptional Elements Bind Proteins:
- Examples of Transcription Factors:

Remember, transcription factors contain DNA binding domains or motifs:
       General Categories: (refer to prev. lecture and textbook for models)
            Helix-Loop-Helix
            Homeodomains
            Leucine Zippers (with basic "fingers")

          Zinc Fingers (there are several types depending on the presence
                of Cys and His residues (C₂H₂, C₄, C₆))
                    - although binding is through zinc-finger monomers, transcription factors
                        tend to have multiple repeats of zinc-finger motifs.

Estrogen Receptor (ER) Binds to Estrogen Response Element (ERE), a promoter-proximal element.

mifepristone (RU486) is a estrogen receptor antagonist
(antagonist: molecule that outcompetes the agonist (estrogen) for the binding site but does not cause hormone-induced effects)

Transcription Factors can form heterocomplexes (heterodimers) with other transcription factors to create a broader range of gene-control.

Acidic Activation Domains: Transcription factors associated with activation tend to have regions rich in acidic amino acids (D, Asp and E, Glu), and often contain S,T,Y (-OH) residues.
        CREB: cAMP response element-binding

Acidic activation domain of CREB forms the part of the protien represented by backbone coils (pink). This region is highly unstructured until cAMP is bound.

Repression Domains, domains that act in the opposite manner as activation domains.
- example in text is WT1 (product of Wilms' tumor (WT1) gene, a repressor of a gene encoding the transcription activator EGR-1. SRF and AP-1 (Jun/Fos) are activators