EXPRESSION AND IN-VITRO TARGETING OF A SUNFLOWER OLEOSIN

Two distinct cDNAs encoding oleosins (oil body proteins) have been ide ntified by degenerate PCR as transcripts present in the developing see ds of sunflower (Helianthus annuus L. cv. Dwarf Sunbred). One (pSOM) o f these is closely related to a reported sunflower oleosin, whilst the other (pSO5) has not been previously described. Different expression patterns were observed for the two cDNAs, pSO5 being expressed earlier than pSOM in seed maturation and oil deposition. The results support the contention that oleosin proteins are synthesised either during or closely after the formation of the oil body. Translation in vitro of s ynthetic oleosin transcripts was enhanced by the addition of microsome s but suppressed by the addition of purified signal recognition partic le (SRP) complex. Deletion of 62 amino acid residues at the C-terminus of the oleosin did not alter the in vitro targeting of the protein to the microsomal membrane. Taken together these data support the idea t hat oleosins are targeted to the ER membrane as part of oil body bioge nesis.