The hemoglobin beta-1 gene of the rabbit was linked to a 244 bp DNA fragment from the beginning of the polyoma virus late region, not including the viral origin of replication. After transfection of such recombinant DNAs into mouse 3T6 and human HeLa cells, the polyoma sequences were found to strongly enhance the level of correct beta-globin gene transcripts over a distance of at least 1400 bp. These findings are similar to those obtained with a segment of DNA from the corresponding region of the SV40 genome (J. Banerji, S. Rusconi and W. Schaffner, 1981, Cell, in press) which, however, shows very limited sequence homology to the polyoma 244 bp segment. Using the same assay, a complete copy of polyoma virus DNA was found to interfere with the enhancement of globin gene expression in a cell type-specific manner which may be due to incorrect transcription. In contrast to the complete polyoma virus genome, the 244 bp DNA fragment will be particularly useful as a component of mammalian expression vectors since it almost exclusively yielded high levels of correct beta-globin gene transcripts.

Sequences which activate polyoma virus DNA replication are located within a region that also includes the transcriptional enhancer. We demonstrate a cis involvement of enhancers in DNA replication by showing that this region can be replaced by other enhancers, in a position- and orientation-independent manner, and that an immunoglobulin gene enhancer confers tissue-specific replicatory ability.

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Transcriptional "enhancers" have been identified in both the monkey virus SV40 and in the mouse polyoma virus. Here we report that these enhancers show a cell type preference. This was done, (i) by assaying for T antigen expression and viral DNA replication of polyoma DNA which contains its own enhancer or the enhancer of SV40 virus, and (ii) by linking either of the two enhancer elements to the rabbit beta 1-globin gene and measuring transient globin expression in mouse and primate cells. The results were consistent in all the assays: In mouse cells the polyoma enhancer is slightly more effective than the SV40 enhancer. However, in primate cells the SV40 enhancer induces a four to six fold higher level of gene expression than does the polyoma enhancer.

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