A TRANSPOSITION-INDUCED MUTANT OF NOSTOC ELLIPSOSPORUM IMPLICATES AN ARGININE-BIOSYNTHETIC GENE IN THE FORMATION OF CYANOPHYCIN GRANULES AND OF FUNCTIONAL HETEROCYSTS AND AKINETES

In strain NE1 of Tn5-1058-mutagenized Nostoc ellipsosporum, the transp oson was found within a gene whose translation product is similar in a mino acid sequence to the arginine-biosynthetic protein N-acetylglutam ate semialdehyde dehydrogenase encoded by argC of Bacillus subtilis. T he argC reported from Anabaena sp. strain PCC 7120 hybridized to a seq uence different from the one interrupted by the transposon in NE1. The newly identified gene from N. ellipsosporum was denoted argL. The arg L mutation renders certain processes in strain NE1 conditionally depen dent on provision of L-arginine. Heterocysts and apparent akinetes tha t formed in the absence of added L-arginine failed to fix dinitrogen o r to germinate, respectively, and lacked granules of cyanophycin, comp osed of copolymers of arginine and aspartic acid. However, apparent ak inetes that differentiated upon growth of the mutant in the presence o f L-arginine plus nitrate formed cyanophycin granules and could regene rate a new culture.