Undermethylation of specific LINE-1 sequences in human cells producing a LINE-1-encoded protein.

Nucleotide sequences near the 5' ends of some long interspersed elements-1 (LINE-1) from Homo sapiens (L1Hs) are undermethylated in cell lines which produce a L1Hs-encoded protein. In contrast, these sequences are methylated in cell lines with little or no detectable L1Hs expression. The fact that the 5' end of L1Hs is differentially methylated in cells exhibiting different levels of L1Hs expression suggests that the methylation state of this region plays a role in L1Hs expression.