CLONING AND SEQUENCE OF CDNAS FOR AN INTRACELLULAR ACID INVERTASE FROM ETIOLATED HYPOCOTYLS OF MUNG BEAN AND EXPRESSION OF THE GENE DURING GROWTH OF SEEDLINGS

Etiolated seedlings of mung bean (Vigna radiata) contain two forms (a heterodimer of 30-kDa and 38-kDa subunits and a 70-kDa monomeric form) of soluble intracellular acid invertase [Arai et al. Plant Cell Physiol. (1991) 32: 1291-1298]. A cDNA for the heterodimeric form was cloned and its nucleotide sequence was determined. The heterodimeric form was synthesized as a single polypeptide with a long leader sequence of 101 amino acids. A sequence resembling a signal peptide, of about 60 amino acids was present at the N-terminus. The extent of similarity in terms of nucleotide and amino acid sequences to carrot acid invertase, the only plant invertase for which the primary structure is known, was 51.1% and 49.6%, respectively. RNA blot analysis showed that a transcript of the gene for acid invertase appeared within 6 h of imbibition of seeds and was accumulated at maximal levels between 9 and 15 h. The time course of the expression of the gene for acid invertase was markedly different from that of the invertase activity itself, and expression of the gene occurred much earlier than the appearance of the enzymatic activity in hypocotyls. The reason for the absence of a correlation between enzymatic activity and the level of the transcript is discussed.