TRANSCRIPT LEVELS FOR A MUNG BEAN CYSTEINE PROTEASE DURING EARLY SEEDLING GROWTH

cDNAs for the major cysteine endopeptidase (CEpase) of mung bean (Vign a radiata [L.] Wilczek) seedling cotyledons have been cloned using gen e-specific primers with the polymerase chain reaction (PCR) in a 3'-RA CE system. A cDNA clone for CEpase, pKL042, that is 1221 bp long exclu ding the poly A tail was isolated. it appears to contain the entire co ding sequence for a 362-residue-long polypeptide. The N-terminal seque nce for the mature CEpase begins at position 128 of the putative trans lation product, suggesting removal of an N-terminal hydrophobic signal peptide and additional sequences to produce the mature protease. Nort hern blot hybridization with CEpase cDNA pKL042 as probe indicates tha t CEpase transcript is not detectable in the cotyledons or the embryon ic axis of dry seeds, but is first detectable in the day 1 cotyledons and in the day 3 axis. The level of CEpase mRNA in both cotyledons and axis increases as growth proceeds. A decline of protease activity, ho wever, is observed after day 3 in the cotyledons, even though the leve l of protease transcripts continues to increase until day 8. Detachmen t of the axis from the cotyledons before day 3 results in the preventi on of the normal increase in both protease activity and CEpase mRNA.