Conservation in the 5' region of the long interspersed mouse L1 repeat: implications of comparative sequence analysis.

A clone of 7.1kb corresponding to the mouse L1 interspersed repeat family was selected for homology to a human interspersed repeat. This clone fairly represents mouse genomic members. Mapping of the clone revealed one common element at both the 5' and 3' ends in a head to tail arrangement, suggesting that at least some long L1 family members are tandemly arranged; genomic studies confirmed the unexpected tandem arrangement of a minor proportion of L1 members. A short SmaI tandem repeat appears to define the 5' end of most L1 family members. SmaI repeats may maintain, via a recursive regulatory function, the transcriptional viability of L1 members after retroposition events. A 2.5kb portion of the mouse L1 repeat that has not been previously sequenced is presented. It is 55-70% homologous to a corresponding portion of the human KpnI repeat family. Comparative sequence analysis revealed that one common open reading frame may conserve potential coding function across species. A second open reading frame bears an asymmetric distribution of codon replacements unlike both genes and pseudogenes. This latter feature could be consistent with a proposed chromosome organization function that is unrelated to peptide expression.