The Chromosome 4 q 21 Gene ( AF - 4 / FEL ) Is Widely Expressed in Normal Tissues and Shows Breakpoint Diversity in t ( 4 ; 1 l ) ( q 21 ; q 23 ) Acute Leukemia

The chromosomal translocation, t (4 ; l l )(q21 ;q23), is the most common type of 1 1 q23 chromosomal abnormality, being highly prevalent in infant acute leukemias and associated with a poor prognosis. The t (4 ; l l ) results in the fusion of an ll q23 gene (MLL, HRX, Htrx-1 , or ALL-1) and a 4q21 gene (AF-4 or FEL). To further evaluate the 4q21 gene and its role in t(4;ll) acute leukemia, we have cloned a 38-kb genomic region and mapped exons of the AF-4 gene. The 4q21 breakpoints in 19 cases of t (4 ; l l ) acute leukemia were analyzed by Southern analysis and pulsedfield gels. Seventeen of the 19 cases had breakpoints on chromosome 4q21 that were scattered in this 38 kb re-