These studies are directed toward several goals. The first is to identify and utilize positive selectable marker genes which may be used to facilitate DNA transfer into mammalian cells. The second is to compare the efficiency of hybrid viruses containing the marker gene to that of DNA introduced by the calcium phosphate precipitate technique in transforming tissue culture or hematopoieticcolony formation under conditions which suggest their direct binding to hematopoietic progenitor cells in vitro. The third is to use viral transcription and/or replication signals to construct a DNA fragment which contains coding portions of a globin gene and which results in substantial globin production in bone marrow cells. A fourth goal is to utilize vectors containing portions of the SV-40 genome to study the function of normal and defective human globin genes in cultured cells.