Two different forms of palindrome resolution in the human genome: deletion or translocation

Regions containing palindromic sequence are known to be susceptible to genomic rearrangement in prokaryotes and eukaryotes. Palindromic AT-rich repeats (PATRR) are hypervariable in the human genome, manifesting size polymorphisms and a propensity to rearrange. Size variations are mainly the result of internal deletions, while two PATRRs on 11q23 and 22q11 (PATRR11 and 22) contribute to generation of the t(11;22), a recurrent constitutional translocation. In this study, we analyzed the PATRR11 sequence of numerous polymorphic alleles in detail. Various types of shorter variants are likely derived from the most frequent ∼450 bp PATRR11 by deletion. Deletion variants possess a significant number of identical nucleotides at their two endpoints, indicating the possible involvement of direct repeats within the PATRR11. Rare variants with insertional alterations involve AT-rich sequences of unknown origin. This is in contrast to palindrome-mediated translocations between PATRRs that manifest smaller deletions and only a limited number of identical nucleotides at the breakpoints. Further, we identified a rare translocation product that has a non-AT-rich insertion of a transcribed gene segment at the translocation breakpoint. Our data suggest that the outcomes of palindrome-mediated re-arrangements reflect distinct molecular pathways; intra-palindrome re-arrangements are possibly dictated by a replication slippage or microhomology-directed repair pathway, and inter-palindrome translocations are likely driven by non-homologous end joining.