SPI1 is a putative oncogene specifically activated in acute murine erythroleukemias, induced by the Friend spleen focus forming virus. It encodes PU.1, an ETS-domain transcription factor normally expressed in all hematopoietic lineages except in T-cells, and is essential for myeloid (osteoclast progenitors) and B-lymphoid cell development. A low concentration of PU.1 induces the B-cell fate, whereas a high concentration promotes macrophage differentiation. (from OMIM 165170 and NCI) [ ]