Effects of ganglioside G M1 on DNA synthesis in isolated nuclei and on the activity of DNA polymerase α derived from S-phase HeLa cells

Abstract

Ganglioside G M1 inhibited either DNA synthesis in isolated nuclei or the activity of DNA polymerase α fractionated from S-phase HeLa cells. The concentrations of G M1 necessary for 50% inhibition were about 5 μM and 10 μM for nuclei and DNA polymerase α, respectively. The G M1 inhibition of the enzyme activity was suppressed by the addition of 0.05% Triton X-100. Neither gangliotetraosylceramide (asialo-G M1) nor free N-acetylneuraminic acid inhibited the enzyme activity. These facts suggest that G M1, probably in the form of micelles, could influence the enzyme activity by behaving as a polyanionic macromolecule. The kinetic studies indicate that the G M1 inhibition of the enzyme activity was not competitive with the substrate, deoxythymidine triphosphate, but rather with the template DNA. Binding of G M1 and DNA polymerase α was suggested by the cocentrifugation of G M1 and the enzyme fraction after their preincubation. It was also observed that other acidic glycolipids, i.e., brain sulphatide and seminolipid, also inhibited the enzyme activity, whilst neutral galactosylceramide did not. The inhibitory influences of these sulphate esters of glycolipids were, similarly to G M1, suppressed by the addition of 0.05% Triton X-100.