DOMAINS WITH TRANSCRIPTIONAL REGULATORY ACTIVITY WITHIN THE ALL1 AND AF4 PROTEINS INVOLVED IN ACUTE-LEUKEMIA

The ALL1 gene, located at chromosome hand 11q23, is involved in acute leukemia through a series of chromosome translocations and fusion to a variety of genes, most frequently to AF4 I and AF9, The fused genes e ncode chimeric proteins, Because the Drosophila homologue of ALL1, tri thorax, is a positive regulator of homeotic genes and acts at the leve l of transcription, it is conceivable that alterations in ALL1 transcr iptional activity may underlie its action in malignant transformation. To begin studying this, we examined the ALL1, AF4, AF9, and AF17 prot eins for the presence of potential transcriptional regulatory domains. This was done hg fusing regions of the proteins to the yeast GAL I DI VA binding domain and assaying their effect on transcription of a repo rter gene, A domain of 55 residues positioned at amino acids 2829-2883 of ALL1 was identified as a very strong activator, Further analysis o f this domain by in vitro mutagenesis pointed to a core of hydrophobic and acidic residues as critical for the activity, An ALL1 domain that repressed transcription of the reporter gene coincided with the seque nce homologous to a segment of DNA methyltransferase. An AF4 polypepti de containing residues 480-560 showed strong activation potential. The C-terminal segment of AF9 spanning amino acids 478-568 transactivated transcription of the reporter gene in HeLa but not in NIH 3T3 cells, These results suggest that ALL1, AF-I, and probably AF9 interact,vith the transcriptional machinery of the cell.