We introduced a human 0-globin gene into murine erythroleukemia (MEL) MATERIALS AND METHODSPlasmid constructions. A detailed account of the construction of pSVX has been presented previously (6). pSVXenwas constructed by first digesting a single long terminal repeat (LTR)-containing plasmid completely with XbaI and partially with PvuIl and then religating the appropriate fragment after addition of SalI linkers. A fragment containing the deleted LTR was then introduced in place of the 3' LTR of pSVX. All P-globin vectors were constructed by inserting a BclI-linkered 3.0-kb human 3-globin fragment, from the HpaI site to the PstI site, into the BamHI site of pSVX or pSVXen-. The human ,-globin gene and the SP6 plasmids used for synthesis of probes complementary to mouse and human f-globin mRNAs were kindly provided by

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We introduced a human beta-globin gene into murine erythroleukemia (MEL) cells by infection with recombinant retroviruses containing the complete genomic globin sequence. The beta-globin gene was correctly regulated during differentiation, steady-state mRNA levels being induced 5- to 30-fold after treatment of the cells with the chemical inducer dimethyl sulfoxide. Studies using vectors which yield integrated proviruses lacking transcriptional enhancer sequences indicated that neither retroviral transcription nor the retroviral enhancer sequences themselves had any obvious effect on expression of the globin gene. Viral RNA expression also appeared inducible, being considerably depressed in uninduced MEL cells but approaching normal wild-type levels after dimethyl sulfoxide treatment. We provide data which suggest that the control point for both repression and subsequent activation of virus expression in MEL cells lies in the viral enhancer element.

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