Nuclear Receptors and Transcription Regulation

What is the primary function of nuclear receptors?

Which of the following is NOT a form in which nuclear receptors can bind to response elements?

Where are steroid hormone receptors located in the absence of a ligand?

What occurs upon ligand binding to a steroid hormone receptor?

How do steroid receptors typically bind to DNA?

What defines a hormone response element (HRE)?

What are the three defining features of a response element?

What happens to the ligand-receptor complex after it translocates into the nucleus?

What is the role of the heat-shock protein (HSP) in relation to steroid hormone receptors?

Nuclear Receptors Overview

Nuclear receptors function as regulatory transcription factors.
They bind to regulatory DNA sequences known as response elements.

Binding Forms of Nuclear Receptors

Can bind as:
- Monomers: Example, steroidogenic factor-1 receptor.
- Homodimers: Example, steroid receptors.
- Heterodimers: Examples, retinoic acid receptor, thyroid hormone receptor, vitamin D receptor, and several orphan nuclear receptors.

Steroid Hormone Receptors

Located in the cytosol in an inactive form stabilized by heat-shock proteins (HSP).
Ligand binding causes dissociation of HSPs, allowing translocation to the nucleus.

Mechanism of Action in the Nucleus

The ligand-receptor complex binds to specific hormone-response elements (HRE) in DNA after nuclear translocation.
Steroid receptors bind as homodimers to inverted repeats with a three-nucleotide spacer sequence.

Characteristics of Hormone Response Elements (HRE)

HREs are specific DNA sequences recognized by receptors with high affinity.
Typically consist of two consensus hexameric half-sites.
Three critical features define a response element:
- Sequence of base pairs in each half-site.
- Number of base pairs separating the half-sites.
- Relative orientation of the half-sites.

Importance of Response Element Recognition

Each dimeric receptor must accurately identify the sequence, spacing, and orientation of the half-sites within the response element to effectively bind DNA.

This quiz explores the role of nuclear receptors as regulatory transcription factors that bind to regulatory DNA sequences known as response elements. It covers the forms in which these receptors can exist, including monomers, homodimers, and heterodimers, as well as their locations and functions within the cell.