A new 5′ sequence associated with mouse L1 elements is representative of a major class of L1 termini

Abstract

Full-length L1 elements have been shown to possess, at their 5 ′ end, tandem repeats called "A" or "F" types. By sequencing the 5′ region of two large L1 copies that did not hybridize to A or F probes, we have identified a new sequence that is found at the 5′ end of many L1 elements and that we call "V." The element characterized has no 200-bp tandem repetitive structure, and the new 5′ sequence is not similar to the A or F sequences. The study of the relationships between the V and L1 sequences has shown that only half of the V (i.e., V-specific 5′) sequences in the genome are linked to the 5′ end of L1 copies. In related rodent species, a comparative study by Southern blot and PCR analysis of the V sequence suggests that this L1 subfamily has an ancient origin and that V sequence isolated from the remainder of the L1 element has been amplified during the evolution of the mouse genome.