Precursor of 5S ribosomal ribonucleic acid in the blue-green alga Anacystis nidulans

Isolation and characterization of 32P-labeled mitochondrial and cytosol ribosomal RNA from germinating wheat embryos

With the aim of preparing highly labeled material, the incorporation of [32P]-orthophosphate into mitochondral and cytosol ribosomal RNA was examined in germinating wheat embryos. Nucleic acids were extracted from mitochondria and from post-mitochondrial supernatant (cytosol) prepared from homogenates of viable embryos (8g) imbibed for 24h in a medium containing [32P]orthophosphate (100mCi). High-molecular-weight ribosomal RNA was selectively precipitated in the presence of 3M NaCl and was further resolved on sucrose density gradients and polyacrylamide gels. Both the mitochondrial and cytosol NaCl-insoluble RNA fractions were found to contain two major radioactive components, corresponding to the large (26S) and small (18S)rRNA species. On non-denaturing gels, these species had apparent molecular weights of 1.3 and 0.67 million daltons (cytosol) and 1.3 and 0.75 million daltons (mitochondrial). The individual, purified [32P]rRNA components (isolated from sucrose gradients) had specific activities of 2--3-10(6) cpm/A260 unit, and were suitable for analysis of nucleotide composition and sequence. By hydrolyzing the individual [32P]rRNA specimens with purified snake venom phosphodiesterase and resolving the products by two-dimensional paper chromatography, it was possible to determine the specific activities (cpm/micronmol) of the four major 5'-nucleotide constituents. The results indicated that there had been no differential 32P-labeling of the nuclear and mitochondrial pools of ribonucleoside 5'-triphosphates (rNTP) during the 24 h imbibition period; however, as previously observed in this system (Lau, R.Y., Kennedy, T.D. and Lane, B.G. (1974) Can. J. Biochem. 52, 1110--1123), there had been unequal 32P-labeling of the individual rNTPs in both the mitochondria and nucleus. The relative specific activities of the 5'-nucleotide constituents of the mitochondrial and cytosol rRNA species were essentially the same, and in the order pA congruent to pU greater than pG greater than pC. By making suitable corrections for these differences in specific activity, the nucleotide composition of each of the [32P]rRNA specimens could be calculated...

Mutational analysis of dark endogenous metabolism in the blue-green bacterium Anacystis nidulans

We describe a mutant (strain 704) of the obligate photoautotroph Anacystis nidulans which behaves like the wild type under continuous illumination but which in the dark rapidly loses viability, respires little, and incorporates label into ribonucleic acid and protein at rates considerably less than observed with the darkened wild type. Extracts of this mutant strain show no detectable 6-phosphogluconate dehydrogenase (EC 1.1.1.44) activity. Spontaneous revertants of mutant 704 were selected as survivors of prolonged incubation in darkness. Of 10 such strains examined, none had regained 6-phosphogluconate dehydrogenase activity, and all had lost detectable glucose-6-phosphate dehydrogenase (EC 1.1.1.49) activity. Although dark survival of these revertants paralleled that of the wild type, rates of dark endogenous respiration and incorporation of labeled precursors into ribonucleic acid were still very low, comparable to those observed with strain 704. These results are consistent with the following hypotheses concerning dark endogenous metabolism in unicellular blue-green bacteria. (i) Although the oxidative pentose phosphate cycle (hexose monophosphate shunt) may play a major role in endogenous metabolism in A. nidulans, as proposed by others, it is not the only pathway capable of providing energy for maintenance of viability in darkness. (ii) Much of the endogenous metabolic activity (respiration and macromolecular synthesis) observed in darkened cultures of wild-type A. nidulans is not required for survival alone, and must therefore serve other functions.