Structural analysis of hnRNP particles approached by in vitro phosphorylation using exogenous protein kinase and l gamma 32 P1 ATP.

Using an exogenous kinase, nuclear ribonucleoprotein complexes with sedimentation coefficients greater than 100S were phosphorylated in vitro before and after treatment with increasing concentrations of NaC1. The phosphorylation pattern of the proteins before raising the NaC1 concentration shows a major group of labelled proteins in the 30 000 to 40 000 MW range. Treatment of the complexes with 400 and 800 mM NaC1 produces a relative increase in the labelling of some polypeptides with the appearance of new labelled bands and the concomitant disappearance of several proteins. Even at the highest salt concentration used (1.2 M), it is still possible to identify a group of labelled polypeptides which are suggested to form the backbone structure of the nuclear RNP complexes.