It has long been accepted that a gene's protein-coding information is contained in only one of its two DNA strands. But in 22 February Nature, Victor Corces and co-workers at the Department of Biology, Johns Hopkins University, overturn this doctrine.

Corces and his colleagues identified a gene important for Drosophila development — modifier of mdg1 or mod(mdg1) — that produces two transcripts, one from each DNA strand. Exons I to IV are transcribed from one DNA strand, whereas exons V and VI are transcribed in the opposite direction from the complementary DNA strand. The two transcripts are subsequently spliced into a single protein-encoding messenger RNA, a phenomenon known as trans-splicing.

The evolutionary process that shaped the gene structure of mod(mdg1) is not known, but genome sequences will reveal whether analogous structures are present in other genes and organisms.

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