ZFP628 interacts with TAF4b in vivo and has transcriptional activator properties. (A) Endogenous TAF4b and TAF4a were immunoprecipitated from P40 testis extract using polyclonal ZFP628 antisera, whereas GAPDH was not. Rabbit preimmune serum was used as a negative control. WB, Western blotting. (B) Relative mouse Zfp628 mRNA levels during testis development and in adult tissues. (C) P35 testis tissue sections. ZFP628 (red) was detected in both germ cells (TRA98 cells in green) and nongerm cells. Blue, DAPI. ZFP628 colocalization with TRA98 occurs most clearly in round spermatids (yellow merge). (D) Domain architecture of Zfp628 highlighting the TAF4b-interacting portion (pink) and a schematic representation of the luciferase reporter assay using the TAF4b-interacting portion of ZFP628 fused to the Gal4 DNA-binding domain. (E) HEK293T cells were transfected with the negative control Gal4-DBD, positive control Gal4-VP16, or Gal4-ZFP628 and reporter constructs, and transcriptional activity was measured by luminescence.