Stability of TAT-NF-Ya in cell culture. (A) Western blot analysis with anti-GST antibody and (B) densitometric quantitation of immunoreactive NF-Ya after exposure to K562 or CD34⁺ peripheral blood cells, in the presence or absence of FBS. TAT-NF-Ya was stable in cell-free, serum-free medium, but the presence of serum in the culture led to complete disappearance of detectable NF-Ya within 15 minutes. In the culture medium without serum, inclusion of hematopoietic cells also led to TAT-NF-Ya degradation, but at a slower rate.