IDENTIFICATION AND SEQUENCE-ANALYSIS OF A RAP GENE FROM THE TRUE SLIME-MOLD PHYSARUM-POLYCEPHALUM

A member of the ras gene superfamily, belonging to the rap family and designated Pprapl, was isolated from a cDNA library from the true slim e mold Physarum polycephalum by plaque hybridization in combination wi th 5'-RACE. The assembled nucleotide sequence of Pprapl (1062 bp) has an open reading frame coding for a protein of 188 amino acids of a cal culated M(r) of 21035. This protein exhibits: (i) a highly conserved G TP binding domain containing a putative effector domain, with the thre onine-for-glutamine substitution characteristic of rap proteins, (ii) a hypervariable domain, and (iii) the CAAX motif. Analysis of the C-te rminal amino acid sequence of Pprap 1 shows that it presumably undergo es geranylgeranylation but is not palmitoylated; however, it contains a lysine-rich domain which might serve as the second membrane localiza tion signal. Pprapl exhibits significantly high amino acid homology wi thin the GTP binding domain with its homologues: Ddrap1 from Dictyoste lium discoideum (92%) and human Rap1A (83%), and relatively low homolo gy (59%) with the Saccharomyces cerevisiae homologue, RSR1. It has als o 59% and 61% homology with the P. polycephalum Ppras1 and Ppras2 prot eins, respectively. This gene is the third member of the ras gene supe rfamily identified in P. polycephalum so far.