Identification and sequence analysis of a rap gene from the true slime mold Physarum polycephalum

摘要

A member of the ras gene superfuinily, belonging lo the nip family ami designated Ppntpl, was isolated from a cDNA library from the true slime mold Physarum polycephalum by plaque hybridization in combination with 5'-RACIi, The assembled nucleotidc sequence of Pprapl (1062 bp) has an open reading frame coding for a protein of IKH amino acids of a calculated M, of 21 035. This protein exhibits: (i) a highly conserved CSTP binding domain containing a putative effector domain, with the tlireonine-foi'-glutamine substitution characteristic of rap proteins, (ii) a hypervariable domain, and (iii) the CAAX motif. Analysis of the C-tenninal amino acid sequence of Pprapl shows that it presumably undergoes geranylgeranylation but is not palmitoylated; however, it contains a lysine-neh domain which might serve as the second membrane localization signal. Pprapl exhibits significantly high amino acid homology within the GTP binding domain with its homologues: Ddrapl from Dictyostcliiim clisrohlcium (92%) and human Rap1A (83%), and relatively low homology (59%) with the Saccharomyces cerevisiae homologue, RSR1. It has also 59% and 61% homology with the P. jwlytrplwlwu PprasI and Ppras2 proteins, respectively. This gene is the third member of the raj gene superfuinily identified in P. polycvpluthim so far.