Cloning and genomic sequence of the Physarum polycephalum Ppras1 gene, a homologue of the ras protooncogene

Abstract

We have cloned the genomic copy of the Pprasl gene, a homologue of the ras proto-oncogene, from the true slime mold Physarum polycephalum. Pprasl contains five small introns, four of which have a high content of pyrimidines. The (dC)-homopolymers present in introns 4 and 5 may be responsible for the observed recA-independent deletion in Pprasl upon amplification of the Pprasl-bearing plasmid by chloramphenicol. Although Pprasl exhibits high amino acid and nucleotide homologies with the DdrasG gene, a homologue of ras from another slime mold, Dictyostelium discoideum, locations and sequences of their introns are quite different. This discordance suggests that introns of the ras genes in these species were acquired independently