TANDEM DUPLICATION VIA LIGHT-STRAND SYNTHESIS MAY PROVIDE A PRECURSORFOR MITOCHONDRIAL GENOMIC REARRANGEMENT

A tandem duplication of the mitochondrial tRNA(Thr) and tRNA(Pro) gene s in the amphisbaenian reptile Bipes biporus is the first case reporte d of a tandem duplication restricted to a single pair of tRNA genes in a vertebrate mitochondrial genome. Such duplications have been predic ted, however, as intermediate steps in the evolution of observed mitoc hondrial genomic rearrangements through errors in light-strand replica tion. The tandem duplication reported here is evolutionarily associate d with displacement of the origin for light-strand replication from it s typical location in vertebrate mitochondrial genomes and loss of the dihydrouridine stem from the tRNA(Cys) gene; these factors implicate light-strand replicational errors in the tandem duplication of genic r egions. Pseudogene formation in tandemly duplicated sequences appears to be an intermediate step in genomic rearrangement. However, formatio n of pseudogenes in the Bipes mitochondrial genome occurs in a pattern that precludes subsequent genomic rearrangement. Functional constrain ts placed on cleavage of mitochondrial transcripts by tRNA genes also may prevent mitochondrial genomic rearrangement.