Our understanding of myeloid factors has been brought about we will focus on how alteration of myeloid transcription by a number of different methods. Initially, myeloid factors were factors (changes in expression and structure) could lead to identified by investigations of known transcription factors, particu-alterations in normal function in myelopoiesis, leading to a larly oncogenes; examples include myb, myc, and the homeobox block in differentiation. In addition, we will discuss those genes. 12a Similarly, a number of factors have been isolated using factors that are involved in normal human myeloid matura- hybridization and/or polymerase chain reaction (PCR) methods tion or human leukemia. Although this review will of neces- based on similarity to known genes, such as MZF-1, with subsequent sity discuss different classes of factors, it does not aim to studies investigating the normal and forced expression of these fac-be an exhaustive compilation or listing of different factors tors in myeloid cells. 29-36 A second approach is subtraction hybridization or differential screening, which identified Egr-1 as a potential and does not intend to be historical. Rather, it will attempt mediator of monocytic development. 25 A third method has been to highlight how recent findings can help to explain normal identification of factors through the analysis of myeloid-specific pro-myeloid development and myeloid leukemia and will focus on certain examples to make important general points. In addition, this review will focus on early events in myeloid