Molecular cloning and structural analysis of genes from Zea mays (L.) coding for members of the ras-related ypt gene family (small guanine nucleotide binding protein/ras gene superfamily)

We have isolated, cloned, and characterized two cDNAs from Zea mays (L.), denoted yptml and yptm2, encoding proteins related to the ypt protein family. Amino acid similarity scores with YPT1 from yeast and ypt from mouse are in the range of 70% for yptml and 74% for yptm2, respec- tively, whereas similarities with p21 ras and other ras-related proteins are <40%. Most amino acid residues showing identity are clustered in the GTP/GDP binding domain. In addition, two cysteine residues close to the C-terminal ends, known to be palmitoylated and necessary for membrane binding in all eukaryotic ras-related proteins that have been characterized so far, are conserved in the maize genes as well. Northern blot hybridization analysis of poly(A)+ mRNA from etiolated maize coleoptiles revealed single mRNA species of approximately the same size as the isolated cDNAs. The gene for yptml is expressed at very low levels in maize coleoptiles and tissue culture cells. The gene for yptm2 is expressed at higher levels and is differentially represented in RNAs isolated from various organs of maize plants, with its highest level in leaves and flowers. The structural similarity of the genes identified sug- gests that they could be involved in the control of secretory processes.