Trans-splicing and gene organization in operons are two peculiar features of C. elegans. Whereas trans-splicing has been shown to be general features of nematodes (1), operons have only been observed in Caenorhabditis and Dolichorhabditis, a genus now called Oscheius(2). Here we describe evidence for the first operon in Pristionchus pacificus. P. pacificus has been established as a satellite organism for comparing developmental processes to Caenorhabditis elegans. These species share a last common ancestor some 100-200 mya years ago and P. pacificus is more distantly related to C. elegans than Oscheius. The genetic and the molecular analysis of developmental processes, such as vulva development, have recently been complemented by a genomic approach (3). We have been studying programmed cell death in P. pacificus and have isolated mutations in two complementation groups, namely
ipa-1 and
ipa-2. Molecular analysis indicated that
ipa-1 corresponds to
Ppa-ced-3 (4). To clone
Ppa-ced-4, we wanted to make use of the fact that
Cel-ced-4 is a member of the operon CEOP3224. In addition to
ced-4, there are four other genes in this operon, with the aldose reductase (AR), C35D10.6 being the most 3' gene in the operon. The orthologue of C35D10.6 was cloned in P. pacificus and placed at the same genetic linkage map position as
ipa-2. Further investigation of the aldose reductase region indicates that the other genes of the C. elegans operon CEOP3224 are not linked to Ppa-AR. However Ppa-AR is located 100 bp downstream of the putative ortholog of ZK1128.4, a gene that is located on the same chromosome in C. elegans. A third, more upstream gene, R144.2, in C. elegans is also located on Chromosome III. Ppa-ZK1128.4 is SL2 spliced, providing further evidence that this group of genes is organized in an operon. The SL2 sequence in P. pacificus differs from the one described in C. elegans and Oscheius. Further analysis is being undertaken to give a representative display of the operon organization in P. pacificus and on operon structure in general. 1.T. Blumenthal, Trends Genet 11, 132-6 (Apr, 1995). 2.D. Evans et al., Proc Natl Acad Sci U S A 94, 9751-6 (Sep 2, 1997). 3.J. Srinivasan et al., Genetics 162, 129-34 (Sep, 2002). 4.R. J. Sommer et al., Development 125, 3865-73. (1998).