Mitochondrial transcription initiation in the crustacean Artemia franciscana

Mitochondrial transcription has been studied in several vertebrate organisms, but so far no report on mitochondrial transcription initiation in invertebrates has been published. Here we present an analysis of transcription initiation sites using in vivo-synthesized transcripts in the crustacean Artemia franciscana. The mitochondrial genome of Artemia has the same coding capacity as most animal mitochondrial genomes, and its overall organization is almost identical to that of Drosophila. Using in vitro capping, RNA mapping techniques and northern hybridization, we have identified a main initiation site for heavy-strand transcription that matches the 5' end of 12S rRNA, on one end of the control region. This nascent RNA has an unusually small size and a highly heterogeneous 5' end. A second potential transcription-initiation site has been located 250 bp upstream of the former, giving rise to a larger, less abundant RNA which also has an heterogeneous 5' end. The two sites have sequence similarity from which a consensus could be derived. Using the same methods we failed to identify any clear initiation site for transcription of the light strand, nevertheless a candidate has been located on the opposite side of the control region, with respect to the heavy-strand initiation sites.