Identification of a novel regulatory element in the c-mos locus that activates transcription in somatic cells.

We have identified a DNA sequence in the 5' flanking sequence of rat c-mos gene which fulfills operational criteria for enhancers, increasing transcription from heterologous promoters in somatic cells. This new enhancer region contains some specific motifs such as two CArG boxes, two M-CAT binding sites and CCAAT consensus sequences. This Upstream Enhancer region (UER) is recognized by distinct protein complexes and particularly CArG2 and M-CAT R1 motifs, which are adjacent in the DNA sequence. Several lines of evidence indicate that none of the two CArG boxes bind to the Serum response factor (SRF). Site-directed mutations of both the CArG2 and M-CAT R1 binding sites suppress their enhancer activity. These results suggest that direct and indirect interactions involving multiple nuclear factors and distinct elements of the UER may be required for its enhancer functions in somatic cells.