Size and structure of the highly repetitive BAM HI element in mice

The BAM HI family of long interspersed DNAs in mice represent as much as 0.5% of the mouse genome. Cloned mouse DNA fragments which contain BAM HI/non-BAM HI junction sequences have been analyzed by restriction mapping and DNA sequencing. It has been found that BAM HI elements: (i) are approximately 7 kilobase pairs in size, (ii) are not bracketed by long repeated sequences analogous to the terminal repeats of proviruses and (iii) contain a poly-dA track at one end. The data strongly suggest that BAM HI elements arose by a process involving RNA intermediates. The beginning of the element, opposite the poly-dA track, contains a 22 base pair sequence exhibiting 65% homology to a ubiquitous mammalian sequence which may play a role in DNA replication (1). The poly-dA end of the element contains BAM5 and R sequences, both of which have been described previously (2,3).