Identification, characterization, and cell specificity of a human LINE-1 promoter.

A constructed human LINE-1 (L1Hs) element containing intact 5' and 3' untranslatable regions and an in-frame fusion between the L1Hs open reading frame 1 and the bacterial lacZ gene (p1LZ) was found to promote the expression of beta-galactosidase in a variety of transiently transfected cell types in tissue culture. Full-length RNA was detected in the transfected cells. Most of the RNA transcripts initiated at or near the beginning of the L1Hs segment. Sequences within the L1Hs segment of p1LZ were sufficient for expression of the reporter gene; however, modulation of the transcriptional regulatory region by upstream sequences was not ruled out. Deletion analysis revealed that the sequences most critical for transcription were located within the first 100 bp of L1Hs. Other sequences within the first 668 bp of L1Hs also contributed to overall expression. Expression of p1LZ was high in human teratocarcinoma cells and low in all other cell types. This pattern of cell-type-specific expression matches the known pattern of endogenous L1Hs transcription in cultured cells.