PHOSPHORYLATION CAN MODULATE THE ASSOCIATION OF DIFFERENT SETS OF RNA-BINDING PROTEINS WITH THE VG1 LOCALIZATION SIGNAL RNA

As assayed by both in vivo and in vitro UV-crosslinking techniques, fo ur RNA binding proteins, with apparent molecular weight of 56, 54, 42, and 40 kilodaltons, associated specifically with the Xenopus Vg1 mRNA localization signal (LS) RNA. The 56 and 54 kD proteins were assigned as the masking proteins described previously, on the basis of their t hermal stability and the effect of phosphorylation on RNA binding acti vity. The 42 and 40 kD proteins associated with the LS RNA at a lower extract concentration than the masking proteins did in vitro. Dephosph orylation will eliminate the RNA binding activities of all four protei ns. However, either raising the extract concentration or phosphorylati ng the extract by the catalytic domain of protein kinase A had opposit e effects on the crosslinking efficiencies of these two sets of RNA bi nding proteins. Phosphorylation might regulate this protein exchange p rocess in vitro. (C) 1997 Academic Press.