ATP Binding Cassette (ABC) transporters constitute one of the largest protein families in both prokaryotes and eukaryotes. Most of these proteins bind ATP and use the energy to drive the transport of various molecules across membranes. Mutations of ABC transporters can result in a number of human diseases or in multidrug resistance in cancer cells. We have identified 60 ABC transporter genes in the C. elegans genome. They are grouped into eight subfamilies by multiple sequence alignment and comparison to human ABC genes. 58 of 60 have putative orthologs in the C. briggsae genome. As a preliminary step to understand how these ABC genes work, we have generated transgenic lines of promoter-GFP constructs for 54 ABC genes in C. elegans using
dpy-5 as a selection marker. 32 of the 54(59.3%) transgenic lines gave observable GFP expression. Expression was more often seen in the B, C and D subfamilies with rates of 86.3%, 66.7% and 80% respectively as opposed to the A, E, F, G and H subfamilies which had rates of 16.7%, 0%, 33%, 30%, 0% respectively. GFP expression was frequently observed for ABC genes on chromosome X, where only two of 17 ABC genes did not produce observable expression. 16 ABC genes are locally duplicated genes. An interesting finding for them was that only two of the 16 genes gave no observable expression, the other 14 ABC genes showed expression in different tissues or stages, suggesting derivation of functional paralogues by tissue or stage specific expression. Many of ABC genes showed expression in intestine in various stages. Expressions in pharyngeal bulbs, neurons and excretory cell are also frequently observed. Mapping of the cis-elements for the coordinate expression will be facilitated by comparing of orthologous promoter regions between C. elegans and C. briggsae. For example, one promoter for C. briggsae ABC gene, Cb-F22E10.1 was examined in C. elegans by transgenic GFP assay. It gave the same expression pattern as that for its C. elegans orthologue, F22E10.1, indicating conserved transcriptional machineries between the two species.