Expression of transposon LINE-1 is relatively human-specific and function of the transcripts may be proliferation-essential

A new 1.7-kb LINE (L1) transcript has been discovered from the cDNA library of human small-cell lung cancer. The nucleotide sequence of 1.7-kb L1 tran script is 98.4% similar to that of open reading frame 2 (ORF2) found in con sensus complete 6.5-kb L1. Although L1 DNA segments could be detected from both genomic DNAs of human and rodent cells by PCR, these L1 transcripts we re not detectable from cellular RNA of rodent cells by RT-PCR and northern hybridization, implying that the expression of L1 was relatively human-spec ific. The functions of L1 transcripts in cells are not yet clear. This pape r shows that L1 transcripts are essential for cell proliferation when deter mined by antisense oligonucleotides. Alternately, L1 transcripts exhibit in all human cells we have examined so far, and they map to all the human chr omosomes. A sequence-similarity search in the GenBank database indicates th at the major sequence of 1.7-kb L1 is integrated in human retinoblastoma (R b), IL-2, and factor VIII genes. Since Rb and factor VIII genes have displa yed high frequency of chromosomal deletions in various cancers and haemophi lia A, the universal integration of long and homologous L1 segments in the genes and all chromosomes may be liable to promote abnormal DNA rearrangeme nt. (C) 1998 Academic Press.