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It has recently been shown that the promoter of a kappa immunoglobulin gene is activated for transcription by a downstream sequence element. Here we mapped the activating element to a resolution of about 20 base pairs by constructing a series of deletions in the cloned kappa gene. After transfection of each deleted gene into myeloma cells, a transient expression assay was used to measure the level of transcription from the kappa promoter. We found that the activating element extends through about 200 base pairs and encompasses a region of sequence that is conserved between mouse and human genes. As successively deeper deletions were made into the conserved region from either the 5' or 3' side, the activating ability was lost gradually rather than abruptly. Although several short segments in this region are homologous to sequences in viral enhancers, they did not seem to play a dominant role in the activating effect. We also found that the activating element remained functional when reversed in orientation or when moved upstream of the kappa gene.

Three cloned segments that hybridize to a region of simian virus 40 (SV40) deoxyribonucleic acid including the origin of replication have been isolated from a monkey genomic library. The primary structure of one segment was previously reported (T. McCutchan and M. Singer, Proc. Natl. Acad. Sci. U.S.A. 78:95-99, 1981). We report here the sequences of the other two segments and a comparison of all three. The SV 40-hybridizing region in each segment is limited to several hundred base pairs. All of the segments contain multiple and disconnected sequences homologous to the region of SV40 directly surrounding the viral replication origin. The number and arrangement of the homologous sequences is different in the three segments. However, the segments have the following features in common: (i) each contains multiple copies of the sequence GGGCGGPuPu, which also appears six times near the origin of SV40; (ii) each contains several strong homologies to the central dyad symmetry of SV40; (iii) each contains a long internal repeat, as does the origin region of SV40. The three SV40-hybridizing segments are members of a larger family of genomic sequences that hybridize well to each other, but not necessarily to SV40.