It has been demonstrated that homozygous mutations at the L(2)gl locus in Drosophila result in the development of tumor in the presumptive adult optic centers of the larval brain and of the imaginal discs. We previously cloned an L(2)gl homologue, Rgl-1, in the rat brain. In this study, we analyzed the capability of Rgl-1 in recovering temperature tolerance in the absence of Saccharomyces cerevisiae Sop genes, yeast homologues of the Drosophila recessive oncogene Lethal (2) giant larvae. The expression of Rgl-1 revealed the recovery of temperature tolerance at 20 degrees C in the absence of Sop genes in Saccharomyces cerevisiae. This indicates that the Rgl-1 cDNA we isolated from the rat brain is highly homologous to Lgl family members and can also substitute the function of Sop proteins for temperature tolerance in Saccharomyces cerevisiae.