Insertion sequences and tandem repetitions as sources of variation in a dispersed repeat family.

Sequencing of ten clones from the major dispersed repeat family of mouse (MIF-1) has identified two novel types of sequence variation. Two clones contain small insertion sequences that are flanked by five base-pair duplications of the target site. A third clone, MIFC70, contains a 20 base-pair insertion composed of four direct repeats of a five base-pair sequence. This insertion may have arisen by successive out-of-register pairing and cross-over events at an ancestral target sequence. MIFC70 is also distinguished by its divergence from the standard MIF-1 sequence; whereas for standard clones of the MIF-1 family inter-copy divergence does not exceed 10%, the divergence between MIFC70 and standard clones is of the order of 26%. MIFC70 may represent an aberrant copy which is now isolated from the bulk of the repeat family and is free to diverge.