Recombination Within the Myelin Basic Protein Gene Created the Dysmyelinating Shiverer Mouse Mutation

Shiverer (shi) is an autosomal recessive mutation in the mouse characterized by an almost total lack of central nervous system myelin. While small amounts of other myelin components are present in the brain of the shi mouse, the four forms of myelin basic protein (MBP) are not detectable. Previous investigations by us and others indicate that the MBP gene has undergone a major rearrangement in the shi mutant. Herein, we report in detail the nature and extent of the rearrangement: a 20-kilobase region within the MBP gene is missing in the mutant. We map the 5' breakpoint of the deletion to the second intron and the 3' breakpoint to a site 2 kilobases beyond the last MBP exon. The junction of the upstream and downstream portions of the gene contains only one nucleotide not accounted for by the wild-type MBP gene sequence. The 3' side of the deletion occurs in the 3rd of 11 tandem repeats of a 31-base-pair sequence. This region is rich in alternating purine and pyrimidine stretches, sequences that have been associated with both Z-DNA structures and gene rearrangements. The recombination junction shares several features with the junctions characterized by Anderson et al. [Anderson, R., Kato, S. & Camerini-Otero, D. (1984) Proc. Natl. Acad. Sci. USA 81, 206-210] in mouse L cells and is consistent with their model for a partially homologous recombination event. The structure of the shi recombination junction suggests that the donor DNA molecules were aligned in a partially homologous region before staggered cutting and joining occurred.