Studies on the structural and functional organization of type II intracisternal A-particle retrovirus elements at the molecular level have continued. We have shown that methylation and association with two defined repetitive sequences appear to play a role in controlling expression of these genes in mouse cells. On the bases on sequence, a peptide representing the viral integrase has been synthesized and used to raise antibodies in rabbits. The antibody will permit us to study the integrase function in a myeloma cell line in which extensive amplification of these IAP sequences has occurred. A cDNA library has been made from this cell line. Clones for further study have been selected on the basis of IAP protein expression as well a sequence homology. Cloning of the integrase gene will allow characterization of this protein.