Chimeric retinoid x receptors and their use in a novel ecdysone receptor-based inducible gene expression system

A gene expression modulation system comprising:

• a) a first gene expression cassette that is capable of being expressed in a host cell comprising a polynucleotide sequence that encodes a first hybrid polypeptide comprising:
• i) a DNA-binding domain that recognizes a response element associated with a gene whose expression is to be modulated;
• and
• ii) a chimeric retinoid X receptor ligand binding domain;
• and
• b) a second gene expression cassette that is capable of being expressed in the host cell comprising a polynucleotide sequence that encodes a second hybrid polypeptide comprising:
• i) a transactivation domain;
• and
• ii) an ecdysone receptor ligand binding domain.

An isolated polynucleotide selected from the group consisting of:

• (a) a polynucleotide encoding a truncated chimeric retinoid X receptor ligand binding domain comprising a truncation mutation, wherein the truncation mutation reduces ligand binding activity of the truncated chimeric retinoid X receptor ligand binding domain;
• (b) a polynucleotide encoding a truncated chimeric retinoid X receptor ligand binding domain comprising a truncation mutation, wherein the truncation mutation reduces steroid binding activity of the truncated chimeric retinoid X receptor ligand binding domain;
• (c) a polynucleotide encoding a truncated chimeric retinoid X receptor ligand binding domain comprising a truncation mutation, wherein the truncation mutation reduces non-steroid binding activity of the truncated chimeric retinoid X receptor ligand binding domain;
• (d) a polynucleotide encoding a truncated chimeric retinoid X receptor ligand binding domain comprising a truncation mutation, wherein the truncation mutation enhances ligand binding activity of the truncated chimeric retinoid X receptor ligand binding domain;
• (e) a polynucleotide encoding a truncated chimeric retinoid X receptor ligand binding domain comprising a truncation mutation, wherein the truncation mutation enhances steroid binding activity of the truncated chimeric retinoid X receptor ligand binding domain;
• (f) a polynucleotide encoding a truncated chimeric retinoid X receptor ligand binding domain comprising a truncation mutation, wherein the truncation mutation enhances non-steroid binding activity of the truncated chimeric retinoid X receptor ligand binding domain;
• (g) a polynucleotide encoding a truncated chimeric retinoid X receptor ligand binding domain comprising a truncation mutation, wherein the truncation mutation increases ligand sensitivity of the truncated chimeric retinoid X receptor ligand binding domain;
• and
• (h) a polynucleotide encoding a truncated chimeric retinoid X receptor ligand binding domain comprising a truncation mutation, wherein the truncation mutation increases ligand sensitivity of a heterodimer, wherein the heterodimer comprises the truncated chimeric retinoid X receptor ligand binding domain and a dimerization partner.

An isolated polynucleotide encoding a chimeric retinoid X receptor ligand binding domain, wherein the polynucleotide comprises a nucleic acid sequence selected from the group consisting of a) SEQ ID NO:

• 45, b) nucleotides 1-348 of SEQ ID NO:
• 13 and nucleotides 268-630 of SEQ ID NO:
• 21, c) nucleotides 1-408 of SEQ ID NO:
• 13 and nucleotides 337-630 of SEQ ID NO:
• 21, d) nucleotides 1-465 of SEQ ID NO:
• 13 and nucleotides 403-630 of SEQ ID NO:
• 21, e) nucleotides 1-555 of SEQ ID NO:
• 13 and nucleotides 490-630 of SEQ ID NO:
• 21, f) nucleotides 1-624 of SEQ ID NO:
• 13 and nucleotides 547-630 of SEQ ID NO:
• 21, g) nucleotides 1-645 of SEQ ID NO:
• 13 and nucleotides 601-630 of SEQ ID NO:
• 21, and h) nucleotides 1-717 of SEQ ID NO:
• 13 and nucleotides 613-630 of SEQ ID NO:
• 21.

An isolated chimeric retinoid X receptor polypeptide comprising an amino acid sequence selected from the group consisting of a) SEQ ID NO:

• 46, b) amino acids 1-116 of SEQ ID NO:
• 13 and amino acids 90-210 of SEQ ID NO:
• 21, c) amino acids 1-136 of SEQ ID NO:
• 13 and amino acids 113-210 of SEQ ID NO:
• 21, d) amino acids 1-155 of SEQ ID NO:
• 13 and amino acids 135-210 of SEQ ID NO:
• 21, e) amino acids 1-185 of SEQ ID NO:
• 13 and amino acids 164-210 of SEQ ID NO:
• 21, f) amino acids 1-208 of SEQ ID NO:
• 13 and amino acids 183-210 of SEQ ID NO:
• 21, g) amino acids 1-215 of SEQ ID NO:
• 13 and amino acids 201-210 of SEQ ID NO:
• 21, and h) amino acids 1-239 of SEQ ID NO:
• 13 and amino acids 205-210 of SEQ ID NO:
• 21.