Cell type-specific transcriptional enhancement in vitro requires the presence of trans-acting factors.

Cell-specific transcriptional enhancement was observed, depending on the enhancer sequences, using nuclear extracts prepared from B-cells, T-cells and HeLa cells. SV40 enhancer stimulated in vitro transcription up to 15-fold in all three cell extracts, whereas transcriptional potentiation in vitro by IgC mu and LPV enhancers was only seen in B- and T-cell extracts. Thus, the cell type specificity seen in vivo can be reproduced in vitro. The transcriptional enhancement requires the presence of enhancer sequences in cis and also of a common factor interacting in trans with all three enhancer sequences. Interestingly, first experiments indicate the additional presence of cellular factors in T-cell and most prominently in HeLa cell extracts which can reduce the enhancer activity of C mu and LPV.