Influence of upstream flanking cellular sequence on the L1 5′-UTR promoter activity. Luciferase reporter assays were performed in both Tera-1 (upper panel) and T47D cells (lower panel). In both panels, promoter activities of the L1.3 5′-UTR in combination with upstream flanking sequences from various other L1 elements are shown in the left part. Upstream flanking sequences from L1C, L1D, L1F, and L1H significantly reduced the L1.3 5′-UTR promoter activity. The upstream flanking sequence from L1M significantly increased the L1.3 5′-UTR promoter activity. The right part depicts promoter activities of various L1 5′-UTRs when flanking cellular sequences are included or excluded from reporter constructs. The tested L1 constructs are about a tenth as active in T47D cells as in Tera-1 cells. Note that the 5′-UTRs display some differences in transcriptional activities when assayed without flanking sequences. However, flanking sequences modulate the 5′-UTR activities considerably. Standard deviations are indicated.
