ELEMENTS IN THE IMMUNOGLOBULIN HEAVY-CHAIN ENHANCER DIRECTLY REGULATESIMIAN-VIRUS 40 ORI-DEPENDENT DNA-REPLICATION

In a previous study, we showed that the immunoglobulin heavy-chain (Ig H) enhancer (IgHe) is near or in an initiation zone of chromosomal DNA replication, which is preferentially active in B cells (K. Ariizumi, Z. Wang, and P. W. Tucker, Proc. Natl. Acad. Sci. USA 90:3695-3699, 19 93). This suggests the existence of a functional relationship between IgHe-mediated transcription and DNA replication. To test this theory, we utilized simian virus 40 (SV40) DNA replication as a model of chrom osomal replication. IgHe or its operationally divisible domains (5'-En , core, and 3'-En) were introduced into SV40 minichromosomes (IgHe-SV4 0). Results of replication assays with IgHe-SV40 replicons indicated t hat the 5'-En and 3'-En activated or suppressed SV40 DNA replication r egardless of the presence of SV40 enhancers or promoters in these repl icons. The activity did not reside in IgHe core sequences. The results suggested that the 5'- and 3'-En regulated SV40 replication through d irect interaction with the origin, not through suppression at the SV40 enhancer and/or promoter. In an effort to identify elements within th e 5'-En motif that contributed to this effect, we found that the E sit e, but not muE5 and muE2 boxes, upregulated DNA replication. Our resul ts provide another possible regulatory function for the 5'-En and 3'-E n domains besides transcriptional suppression of IgHe.