ANALYSIS OF THE IN-VITRO TRANSLATION PRODUCT OF A NOVEL-TYPE DROSOPHILA-MELANOGASTER ALDOLASE MESSENGER-RNA IN WHICH 2 CARBOXYL-TERMINAL EXONS REMAIN UNSPLICED

Drosophila melanogaster generates three different types of aldolase mR NAs from a single gene by selective usage of the triplicate exons 4 (4 alpha, 4 beta, and 4 gamma), which encode three different isozymes ha ving respective carboxyl termini. We have found the presence of a nove l-type mRNA (named alpha(beta)) in which two final exons, 4 alpha and 4 beta, were retained unspliced, Herein, a cDNA clone containing the a lpha(beta) sequence was inserted into pINIII and expressed in an Esche richia coil system, The product, which exhibited aldolase activity, wa s found to be isozyme alpha from the primary structure and the enzymol ogical properties, with the 4 alpha sequence alone being present as th e carboxyl terminus. In tissues of D. melanogaster, the production of mRNA encoding exon 4 alpha is known to be restrained to a low level. T his may be understood by the fact that the aldolase gene of this speci es does not have a typical poly(A) signal at the 3' end in exon 4 alph a. Instead, the transcript-encoding exons, 4 alpha and 4 beta, might b e produced when AATATA, which resides downstream of the coding frame i n exon 4 beta, is recognized as a poly(A) signal during RNA processing . (C) 1995 Academic Press, Inc.