CLONING AND CHARACTERIZATION OF A DEVELOPMENTALLY-REGULATED SEA-URCHIN CDNA-ENCODING GLUTAMINE-SYNTHETASE

A 2935-bp cDNA clone encoding glutamine synthetase (GS) was isolated f rom a cDNA library prepared from fourblastomere Paracentrotus lividus sea urchin embryos. The sequence consists of a 75-bp 5' untranslated r egion (5'-UTR) followed by a 1095-bp coding region corresponding to a 365-amino-acid (aa) protein, a 1747-bp 3'-UTR and a terminal 18-bp pol y(A) tail. The encoded protein shows about 66% identical residues, as compared with human and lobster class-II GS, The sequence contains the Mn2+-binding aa and the highly conserved aa regions observed in other GS. Northern blot analyses show that the GS mRNA is present in the se a urchin egg and is developmentally regulated in the embryo.