Binding of P1,P4-bis(5'-guanosyl)tetraphosphate to brain

A brain preparation, consisting of nuclei and perikarya, was able to bind tritium-labeled diguanosine tetraphosphate ([3H]Gp4G). The binding was linear with both time and amount of extract and apparently presented two dissociation constant values (KD) of 0.16 and 0.6 microM, respectively, as determined by equilibrium binding experiments. Inhibition of [3H]Gp4G specific binding by 50% at equilibrium was accomplished by cold Gp4G, guanosine 5'-tetraphosphate, diguanosine triphosphate, and GTP at 0.7, 2.8, 3.1, and 10 microM concentrations, respectively. Diadenosine tetraphosphate (Ap4A) at concentrations up to 100 microM did not affect the observed binding of [3H]Gp4G to brain. These results suggest that this binding is specific and requires the existence of 4 phosphates plus at least 1 guanosine residue in the molecule. The binding of Gp4G to brain increased with time of development reaching a plateau at about 20 days after birth. The data are discussed in relation to previous results on the binding of Ap4A to brain and to DNA polymerase-alpha (Grummt, F., Waltl, G., Jantzen, H-M., Hamprecht, K., Huebscher, U., and Kuenzle, C. C. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 6081-6085; Rapaport, E., Zamecnik, P. C., and Baril, E. F. (1981) Proct. Natl. Acad. Sci. U. S. A. 78, 838-842).