DUF23 is a Domain of Unknown Function consisting of ~270aa, which is found in predicted proteins encoded by at least 60 genes in the genome of C. elegans. One of these, GALT-1, has been shown to have galactosyltransferase activity and confers sensitivity to a fungal toxin (Titz et al. 2009, PMID: 1958195). Another is BAH-1, which confers sensitivity to head biofilm formation on lawns of Yersinia pseudotuberculosis (the Bah phenotype; Drace et al. 2009, PMID: 1970590). We have found that two other genes with Bah mutant phenotypes,
bah-2 and
srf-2, also encode DUF23 proteins. In addition, selections for mutants resistant to the coryneform surface pathogen Leucobacter Verde1 (Hodgkin et al. 2013, PMID: 24207844) have identified another DUF23 gene, called
subs-4. Null mutants of
subs-4 die at a late embryonic stage, probably as a result of epidermal defects. However,
srf-2;
subs-4 double mutants are viable, small and resistant to Verde1, unlike
srf-2 single mutants which are killed by Verde1. This surprising effect implies interactions between DUF23 proteins in forming normal surface structures and surface coat. Related DUF23 genes are under further investigation. Mutants of
bah-1 and
bah-2 are abnormal in their interaction with Leucobacter Verde1 as well as with Yersinia, because they rapidly form "tangles" of aggregated worms when exposed to Verde1 in liquid, rather than the "stars" formed by wildtype worms. These observations suggest that nematode DUF23 proteins are frequently involved in determining surface properties, perhaps by affecting glycosylation. DUF23-encoding genes occur also in plants, insects and some vertebrates, but their functions in these organisms are unknown.