The complete family of genes encoding G proteins of Caenorhabditis elegans

Caenorhabditis elegans is the first animal whose genomic sequence has been determined(1). One of the new possibilities in post-sequence genetics is the analysis of complete gene families at once. We studied the family of heterotrimeric G proteins(2). C, elegans has 20 G alpha, 2 G beta and 2 G gamma genes. There is 1 homologue of each of the 4 mammalian classes of G alpha genes, G(i)/G(o)alpha, G(s)alpha, G(q)alpha and G(12)alpha, and there are 16 new alpha genes. Although the conserved G alpha subunits are expressed in many neurons and muscle cells(3-7), GFP fusions indicate that 14 new G alpha genes are expressed almost exclusively in a small subset of the chemosensory neurons of C, elegans(8,9). We generated loss-of-function alleles using target-selected gene inactivation(10,11). None of the amphid-expressed genes are essential for viability, and only four show any detectable phenotype (chemotaxis defects), suggesting extensive functional redundancy. On the basis of functional analysis, the 20 genes encoding G alpha proteins can be divided into two groups: those that encode subunits affecting muscle activity (homologues of G(i)/G(o)alpha G(s)alpha and G(q); refs 3-6), and those (14 new genes) that encode proteins most likely involved in perception.