Gene fusions for control of genetically modified cells

A polynucleotide comprising a polynucleotide sequence encoding a fusion protein, the fusion protein comprising a truncated BH3-interacting domain death agonist (tBID) polypeptide and a steroid hormone receptor (SHR) domain polypeptide, wherein the tBID polypeptide comprises a deletion of BID helix 1 and BID helix 2,

• and wherein any of A-D is true:
• a) wherein the tBID polypeptide shares at least 95% identity to SEQ ID NO:
• 1;
• b) wherein the tBID polypeptide shares at least 95% identity to SEQ ID NO:
• 93;
• c) wherein the fusion protein shares at least 95% identity to ESR1-D (SEQ ID NO:
• 4);
• d) wherein the fusion protein shares at least 95% identity to D-ESR1 (SEQ ID NO:
• 5);
• e) wherein the fusion protein shares at least 95% identity to ESR1-C(SEQ ID NO:
• 6);
• f) wherein the fusion protein shares at least 95% identity to C-ESR1 (SEQ ID NO:
• 7);
• or
• g) wherein the fusion protein shares at least 95% identity to H-ESR1 (SEQ ID NO:
• 97).