Protein Synthesis and Degradation in Anabaena During Nitrogen Starvation

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Abstract
N starvation and heterocyst development were induced in the cyanobacterium Anabaena 7120 by growth in N-free medium or by treatment with the amino acid analog methionine sulfoximine. During the first 6 h of N deprivation, amino acid levels and rates of protein synthesis, as measured by the incorporation of [3H]leucine, decreased to 50-70% of those in NH3-grown organisms; after this time there was no difference between the rates of protein synthesis in NH3-grown and N-starved cultures. The period 4-12 h after the onset of starvation was marked by the release of [3H]leucine from previously labeled proteins at a rate 6-7.5 times that of NH3-grown organisms. These results show that N starvation in cyanobacteria causes a reduction in protein synthesis and leads to the rapid degradation of storage proteins. In rapidly growing Anabaena 7120, the doubling time for total cell protein was 14.9 .+-. 1.0 h and the half-life was 139 .+-. 88 h.