A 10kb segment including exons 7 and 8 (but not the splice acceptor site of exon 7) was replaced with lacZ coding sequence followed by a PGK-neomycin resistance gene. A fusion protein is produced which contains the N-terminal 242 amino acids of Runx1, including its nuclear localization sequences, combined with beta-galactosidase sequences. The fusion protein lacks Runx1 function.