Part of the regulatory region of βTub85D drives expression of a mutant form of HtrA2 in which the serine at amino acid 266 has been replaced by alanine.
Expression of HtrA2S266A.βTub85D fails to rescue the sterility seen in HtrA2NSO/Df(3R)ED5644 mutant males. In these males the seminal vesicles are empty and no motile sperm are observed.