Time courses of p53 and p21 accumulation in cultured, folate-deficient erythroblasts. Folate-deficient erythroblasts were cultured in either control medium or folate-deficient medium. At the hours of culture shown atop each lane, cells were collected and lysed by sonication and boiling in SDS-PAGE sample buffer (Laemmli). The samples were separated by SDS-PAGE. Shown are Western blots of gels that were loaded with 50 μg protein per lane. The blots were probed with antibodies to p53 and p21 and then developed with enhanced chemiluminescence.