Isolation and characterization of cytoplasmic poly(A) polymerase from cryptobiotic gastrulae of Artemia salina

Poly(A) polymerase from Escherichia coli adenylylates the 3'-hydroxyl residue of nucleosides, nucleoside 5'-phosphates and nucleoside(5')oligophospho(5')nucleosides (NpnN)

The capacity of Escherichia coli poly(A) polymerase to adenylylate the 3'-OH residue of a variety of nucleosides, nucleoside 5'-phosphates and dinucleotides of the type nucleoside(5')oligophospho(5')nucleoside is described here for the first time. Using micromolar concentrations of [alpha-32P]ATP, the following nucleosides/nucleotides were found to be substrates of the reaction: guanosine, AMP, CMP, GMP, IMP, GDP, CTP, dGTP, GTP, XTP, adenosine(5')diphospho(5')adenosine (Ap2A), adenosine (5')triphospho(5')adenosine (Ap3A), adenosine(5')tetraphospho(5')adenosine (Ap4A), adenosine(5')pentaphospho(5')adenosine (Ap5A), guanosine(5')diphospho(5') guanosine (Gp2G), guanosine(5')triphospho(5')guanosine (Gp3G), guanosine(5')tetraphospho(5')guanosine (Gp4G), and guanosine(5')pentaphospho(5')guanosine (Gp5G). The synthesized products were analysed by TLC or HPLC and characterized by their UV spectra, and by treatment with alkaline phosphatase and snake venom phosphodiesterase. The presence of 1 mM GMP inhibited competitively the polyadenylylation of tRNA. We hypothesize that the type of methods used to measure polyadenylation of RNA is the reason why this novel property of E. coli poly(A) polymerase has not been observed previously.

Diadenosine 5",5"'P1,P4-tetraphosphatase in Drosophila embryos: developmental regulation and characterization

1. An enzyme has been isolated from Drosophila embryos which specifically hydrolyzes dinucleoside tetraphosphates to the corresponding nucleoside tri- and tetraphosphates, with Km values around 4 microM. 2. Nucleoside mono-, di- and triphosphates are competitive inhibitors with K1 values i the 0.01 mM range. 3. The inhibition is particularly strong by adenosine tetraphosphate (Ki = 10 nM). 4. The enzyme is maximally active at pH 7.5 and is quite stable at acid pH. 5. The enzyme requires divalent cations for activity: Co(2+) much greater than [corrected] Mn(2+) Mg(2+) x Co(2+) stimulated about 90-fold at 6 mM. 6. The specific stimulation by Co(2+) has been described before, but at lower concentrations, for the enzyme of procaryotes which splits diadenosine tetraphosphate symmetrically. Zn(2+) and Ca(2+) are inhibitors of the Drosophila enzyme. Co(2+) is also inhibitor in the presence of Mg(2+). 7. The Drosophila enzyme has essential sulphydryl group(s) and a molecular weight of 26,000. 8. Diadenosine tetraphosphatase is present in mature oocytes and increases after fertilization to reach a peak 1.5 hr later. 9. From this time to 3.5 hr the activity decreased to remain at a plateau until the end of embryogenesis. 10. The profile of activity is compatible with its involvement in the regulation of nuclear division.

Lipovitellin inhibition of Artemia trypsin-like proteinase: a role for a storage protein in regulating proteinase activity during development

Artemia trypsin-like proteinase has been reported previously to be highly inhibited in the embryo (B. Ezquieta and C.G. Vallejo (1985) Comp. Biochem. Physiol. 82B, 731-736). We report now that Artemia lipovitellin, the major storage protein complex, inhibits the proteinase. We have carried out an in vitro study of the characteristics of the inhibition. Lipovitellin, a glycolipoprotein of high molecular mass (650 kDa), behaves initially as a substrate but after a limited proteolysis becomes an inhibitor of the proteinase. The enzyme although inhibited in the hydrolysis of the protein substrate retains activity toward low molecular weight substrates. The residual activity on the protein substrate is inhibited by small inhibitors of the proteinase. These features of lipovitellin inhibition are reminiscent of the trap mechanism of alpha 2-macroglobulin inhibition, previously proposed as suitable for regulating proteolytic processes involved in development. Inhibition by lipovitellin is greater at low temperatures and has been determined at 17 and 37 degrees C, in the lower and higher part of the viable temperature range of Artemia development. At high temperature the proteinase hydrolyzes the inhibitor quite efficiently and the inhibition is lower. The inhibition by lipovitellin appears specific for Artemia trypsin-like proteinase when compared with other control pairs protein/proteinase. The results may provide support for an additional role of storage proteins as developmental inhibitors of proteinases.