Isolation, characterization, and functional analysis of a novel cDNA cloneencoding a small rubber particle protein from Hevea brasiliensis

Biochemical evidence reported so far suggests that rubber synthesis takes p lace on the surface of rubber particles suspended in the latex of Hevea bra siliensis. We have isolated and characterized a cDNA clone that encodes a p rotein tightly bound on a small rubber particle. We named this protein smal l rubber particle protein (SRPP), Prior to this study, this protein was kno wn as a latex allergen, and only its partial amino acid sequence was report ed. Sequence analysis revealed that this protein is highly homologous to th e rubber elongation factor and the Phaseolus vulgaris stress-related protei n. Southern and Northern analyses indicate that the protein is encoded by a single gene and highly expressed in latex. An allergenicity test using the recombinant protein confirmed that the cloned cDNA encodes the known 24-kD a latex allergen. Neither ethylene stimulation nor wounding changed the tra nscript level of the SRPP gene in H. brasiliensis. An in vitro rubber assay showed that the protein plays a positive role in rubber biosynthesis. Ther efore, it is likely that SRPP is a part of the rubber biosynthesis machiner y, if not the rubber polymerase, along with the rubber elongation factor.