Formation in the dark, of virus-induced deoxyribonuclease activity in Anacystis nidulans, an obligate photoautotroph

Interaction between hysteretic regulation and redox modulation of glucose-6-phosphate dehydrogenase from Anacystis nidulans

The glucose-6-phosphate dehydrogenase (G6PDH) of cyanobacteria is a hysteretic enzyme which is also subject to redox modulation [FEBS Lett. 126 (1981) 85-88]. We have found that the hysteretic and redox properties of G6PDH exhibit specific interactions: (1) The hysteretic forms of G6PDH ('hypoactive' in equilibrium 'hyperactive'), obtained at pH 7.5 and 6.5, respectively, differ in their redox properties. The 'hypoactive' form is easily activated by oxidation whereas the 'hyperactive' form is easily deactivated by reduction. (2) At low G6P concentrations (greater than 1 mM) only the oxidized form of G6PDH has significant activity. An increase in G6P level diminishes the difference between the activity of oxidized and reduced G6PDH forms.

Redox modulation of a phosphatase from Anacystis nidulans

Ascorbic acid (AA) increased the phosphatase activity (pH 6.8) in 10,000 g supernatants from Anacystis nidulans. The enzyme activated by AA was deactivated by dehydroascorbic acid (DHAA). The modulation by AA/DHAA of phosphatase activity in Anacystis appears to be specific; a number of other redox compounds, known to modulate other enzymes, had no effect on the Anacystis phosphatase. A purified phosphatase preparation from Anacystis was also deactivated by DHAA. In contrast, the purified enzyme was not activated by AA, suggesting that a factor mediating the effect of AA was lost during purification. Another factor was found to protect the purified phosphatase against deactivation by DHAA. The enzyme was characterized as a phosphatase with a broad substrate specificity, an apparent molecular weight of 19,000, and a pH optimum of 6.0-7.0. Dialysis of the enzyme preparation against EDTA abolished the phosphatase activity which could be restored by Zn(2+) ions and partially restored by Co(2+) ions. Crude extracts also contained a latent enzyme, the phosphatase activity of which could be detected in the presence of Co(2+) ions only. Zn(2+) ions did not activate this enzymatically inactive protein. The Co(2+)-dependent phosphatase had an apparent mol. wt. of 40,000, a broad substrate specificity, and an alkaline pH-optimum. Infection of Anacystis cultures by cyanophage AS-1 resulted in a decrease in phosphatase activity. The enzyme present in 10,000 g supernatants from infected cells could not be modulated by the AA/DHAA system.

Isolation and properties of an isocitrate dehydrogenase from Anacystis nidulans

A NADP+-specific isocitrate dehydrogenase (EC 1.1.1.42) was isolated and purified over 400-fold from Anacystis nidulans. The enzyme activity responded slowly to rapid changes in ligand (NADP+, isocitrate, Mg2+-ions) or enzyme concentration as well as to rapid changes in temperature. These are properties characteristic of the hysteretic enzymes. In addition, the enzyme activity was subject to product (alpha-ketoglutarate) inhibition. ATP, ADP and CDP also inhibited the enzyme. Unlike several other cyanobacterial enzymes, the isocitrate dehydrogenase of Anacystis is not under redox control.

Bacteriophage infection interferes with guanosine 3'-diphosphate-5'-diphosphate accumulation induced by energy and nitrogen starvation in the cyanobacterium Anacystis nidulans

Anacystis nidulans accumulates large amounts of guanosine 3'-diphosphate-5'-diphosphate (ppGpp) upon nutritional or energy starvation induced by light-to-dark shift, treatment with carbonylcyanide-m-chlorophenylhydrazone (an uncoupler), or treatment with L-methionine-DL-sulfoximine (an inducer of nitrogen starvation). In contrast to healthy A. nidulans cells, those infected by AS-1 cyanophage do not respond with ppGpp accumulation when starved after about one-third of the complete infection cycle, except, to some extent, under extreme conditions when both nitrogen deprivation and energy deprivation are induced simultaneously (darkening plus L-methionine-DL-sulfoximine treatment). In contrast to cyanophage infection in Anacystis, infection with T4 phage of Escherichia coli CP 78 cells does not affect their accumulation of ppGpp under treatments identical with or similar to those applied in the experiments with Anacystis. This difference in response of phage-infected heterotrophic and photoautotrophic cells to starvation seems to reflect differences in control of nutritional or energy metabolism rather than differences in ability to synthesize ppGpp.

Effect of light on the attachment of cyanophage AS-1 to Anacystis nidulans

The effect of illumination on the extent and kinetics of the adsorption of cyanophage AS-1 to the blue-green alga (cyanobacterium) Anacystis nidulans was studied by using 32P-labeled phage. The initial rate of adsorption was not significantly affected by light. However, at Na+ levels used ordinarily to culture the alga ([Na+] = 11.7 mM), the total amount of phage adsorbed was doubled in the illuminated cultures, as compared with the dark-grown ones, over a wide range of multiplicities of infection (0.05 to 20). Upon a 10-fold increase in Na+ concentration in the medium ([Na+] = 0.11 M), the dark adsorption of the phage increased to the level of light adsorption found in low Na+ medium. The effects on phage adsorption of high Na+ concentration and light were not additive.

The postmaturational cleavage of 23 S ribosomal RNA in Anacystis nidulans is inhibited by infection with cyanophage AS-1

The 23S (1.1 X 10(6) mol.wt.) rRNA of Anacystis nidulans undergoes postmaturational cleavage to produce 0.9 X 10(6) and 0.2 X 10(6) molecular species. We have provided evidence in double labelling experiments, in which we could distinguish between the fate of molecules synthesized before and after infection, respectively, that infection with cyanophage AS-1 abruptly and completely inhibits the cleavage of 23S rRNA in Anacystis cells.