The complete murine immunoglobulin class switch region of the alpha heavy chain gene-hierarchic repetitive structure and recombination breakpoints.

A 7255-base pair (bp) sequence, including the previously sequenced murine segments of I alpha, S alpha, and C alpha, has been completed. Homology matrix comparison revealed a switch repetitive region of 4.2 kilobases (kb) composed of 20-80-bp homology runs, including the previously assigned S alpha region. We distinguished several stretches of duplication, i.e. the central 0.8-kb repetitive region, with some 80-bp staggered consensus repeats containing 20-30-bp subsets, made up of the primordial pentamers CTG(A/G)G. All the break-points of the S alpha switch recombination, including those generated by the translocation of the c-myc protooncogene and those catalyzed by bacterial extracts, are located within the consensus sequence subsets of the 4.2-kb repetitive region.