Isolation and Characterization of cDNAs That Encode Eleven Small GTP-Binding Proteins fromPisum sativum

摘要

Eleven cDNA clones (praltopra9A, pra9B, andpra9C) were isolated from a pea (Pisum sativum) leaf cDNA library which were similar to small GTP-binding proteins. These cDNAs encoded proteins of 22–25 kDa, which exhibited 45–92%identity to one another at the amino acid level. The putative proteins included the characteristic sequences ofras-related small GTP-binding proteins: four conserved domains involved in binding of GTP/GDP; an effector domain; and cysteine residues at the COOH-terminus. Indeed, thepra6protein, expressed inEscherichia coli, clearly showed GTP-binding activity. Phylogenetic analysis showed that these clones can be classified into two subgroups: proteins encoded bypra1topra7being related toypt3andrabllproteins; and proteins encoded bypra8,pra9A,pra9B, andpra9Cbeing related toYPT1andrab1proteins. The effector sequences in these two subgroups were different. RNA gel blot analysis showed that most of the corresponding genes are differentially expressed in pea leaves and roots. Variations in expression were also observed for structurally related ge