The L1 family (KpnI family) sequence near the 3' end of human beta-globin gene may have been derived from an active L1 sequence.

We previously reported that some L1 family (KpnI family) members are closely associated with the Alu family sequence. To understand the details of the L1-Alu association, the structure of a L1-Alu unit downstream from the beta-globin gene was compared between human and primates. The results revealed that the L1-Alu-associated sequence was formed by the insertion of the L1 sequence, T beta G41, into the 3' poly A tract of the preexisting Alu family sequence. It was estimated that the T beta G41 sequence was inserted after the divergence of Old World monkeys and hominoids and before the divergence of orang-utan and common ancestor of other higher hominoids. From the calculation of the mutation rates of L1 sequences, it was suggested that the T beta G41 was derived from an active L1 sequence which was able to encode reverse transcriptase-related protein.