Putative origin and function of the intergenic region between COI and COII of Apis mellifera L. mitochondrial DNA

The mitochondrial genome of honeybees is characterized by the presence of a long intergenic sequence located between the COI and COII genes. In addition, the length of this sequence varies between and within subspecies. Four length categories (200, 250, 450 and 650 bp) have been found in 63 sampled colonies. Analysis of the sequence of the largest type reveals the existence of two units: P (54 bp, 100% A + T) and Q (196 bp, 93.4% A + T). The lengths encountered in the sample are explained by the following combinations: Q, PQ, PQQ and PQQQ. According to similarities in primary and secondary structures, the sequence Q has been divided into three parts: Q1 (similar to the 3' end of the COI gene), Q2 (similar to the neighboring tRNA(leu) gene) and Q3 (highly similar to the P sequence). These relationships led us to hypothesize that these sequences, which do not have any counterpart in Drosophila yakuba mitochondrial DNA (mtDNA), arose by tandem duplication. The usual location of length variation in mtDNA control regions prompted us to examine the hypothesis that this COI-COII intergenic region might contain an origin of replication. High A + T content, stability profile, hairpin and cloverleaf putative secondary structures are all in favor of this hypothesis.