The activity of the endogenous galactosyltransferase 1 (GalT1) and sialyltransferase 1 (SialT1) of CHO-K1 cells were increased 1.4

and 2.3 fold, respectively, in a cell clone (ST18) stably expressing sialytransferase 2 (SialT2). Here we show, by biochemical assays,

that this activation was neither due to the appearance of activators (i.e. glycolipid products) nor to evident stabilization of GalT1 and

SialT1. Real-time PCR experiments failed to demonstrate transcriptional activation of GalT1 and SialT1 genes. Since SialT2

forms a complex with GalT1 and SialT1 with participation of their N-terminal domains (Ntd), we looked for the activation of GalT1

and SialT1 in a cell clone that stably express the Ntd of SialT2 fused to the GFP. Results showed a poor activity of the Ntd of SialT2 to

activate GalT1 and SialT1. Taken together, these results indicate that activation of GalT1 and SialT1 by SialT2 is associated to its

lumenal domain, and reinforce the possibility previously advanced of an effect on the topological organization of these enzymes along

the Golgi complex (Uliana et al., 2006).