ANALYSIS OF EXPRESSION OF THE ARGC AND ARGD GENES IN THE CYANOBACTERIUM ANABAENA SP STRAIN PCC 7120

A cloned DNA fragment from Anabaena sp. strain PCC 7120 that complements an arginine auxotrophic mutant from the same organism,vas found to include an open reading frame encoding a 427-residue polypeptide that is homologous to N-acetylornithine aminotransferase from Bacillus subtilis, Escherichia coli, and Saccharomyces cerevisiae. The gene encoding N-acetyloynithine aminotransferase in bacteria has been named argD. The expression of Anabaena sp. strain PCC 7120 argD, its well as of argC, was analyzed at the mRNA level. Both genes were transcribed as monocistronic mRNAs, and their expression was not affected by exogenously added arginine. Primer extension analysis identified transcription start points for both genes which were preceded by sequences similar to that of the E. coli RNA polymerase sigma(70) consensus promoter. A second transcription start point for the argD gene that is not preceded by a sigma 70 consensus promoter was detected in dinitrogen-grown cultures.