Cellular localization and expression of template-activating factor I in different cell types.

Template-activating factors I (TAF-I) alpha and beta have been identified as chromatin remodeling factors from human HeLa cells. TAF-I beta corresponds to the protein encoded by the set gene, which was found in an acute undifferentiated leukemia as a fusion version with the can gene via chromosomal translocation. To determine the localization of TAF-I, we raised both polyclonal and monoclonal antibodies against TAF-I. The proteins that react to the antibodies are present not only in human cells but also in mouse, frog, insect, and yeast cells. The mouse TAF-I homologue is ubiquitous in a variety of tissue cells, including liver, kidney, spleen, lung, heart, and brain. It is of interest that the amounts of TAF-I alpha and beta vary among hemopoietic cells and some specific cell types do not contain TAF-I alpha. The level of the TAF-I proteins does not change significantly during the cell cycle progression in either HeLa cells synchronized with an excess concentration of thymidine or NIH 3T3 cells released from the serum-depleted state. TAF-I is predominantly located in nuclei, while TAF-I that is devoid of its acidic region, the region which is essential for the TAF-I activity, shows both nuclear and cytoplasmic localization. The localization of TAF-I in conjunction with the regulation of its activity is discussed.