THE MYB AND AHI-1 GENES ARE PHYSICALLY VERY CLOSELY LINKED ON MOUSE CHROMOSOME-10

Ahi-1 has previously been identified as a common helper provirus integ ration site on mouse Chromosome (Chr) 10 in 16% of Abelson pre-B-cell lymphomas and shown to be closely linked to the Myb protooncogene. By using long-range restriction mapping, we have mapped the Myb and Ahi-1 regions within a 120-kbp DNA fragment. The Ahi-1 region is located ap proximately 35 kbp downstream of the Myb gene. A further comfirmation of this finding was obtained by screening a mouse YAC library. The thr ee positive clones obtained contained both the Myb and Ahi-1 gene sequ ences. To test whether provirus integration in the Ahi-1 region enhanc es the expression of Myb by a cis-acting mechanism, we have also exami ned Myb gene expression in A-MuLV-induced pre-B-lymphomas. Our data ha ve revealed that there is no clear evidence for such activation in the tumors we have tested, indicating that provirus insertion in the Ahi- 1 region is activating a novel gene, apparently involved in tumor form ation.