We shall complete a detailed characterization of the replication requirements of specific reiteration mutants of simian virus 40. These mutants have tandem repeats of small segments of the SV40 genome including the initiation site for DNA replication. Using restriction endonucleases and electron microscopy we will physically map these mutant DNAs and compare their DNA structure to that of SV40 DNA. These studies of reiteration mutants have led us into a related series of experiments on the fate of small segments of phage lambda DNA in monkey cells. In this work, we covalently joined two segments from the immunity region of lambda DNA to SV40 (vector) DNA segments isolated from different reiteration mutants. Our subsequent studies will explore possible transcription and translation of the lambda DNA information in monkey cells. Finally, we have succeeded in transforming primary human endothelial cells with SV40 DNA. Studies of the phenotypic properties of these cells will be undertaken.