Table 1.

The C1 hnRNP protein hyperphosphorylation activity is distinct from several known kinases

Inhibitor/activator*	Effect on RNA-dependent C1 hnRNP protein phosphorylation†
2,3-Bisphosphoglycerate (CKII↓)	0
Quercetin (CKII↓)	0
H-7 (PKA↓)	0
Staurosporine (PKC↓)‡	0
EGTA (CaM-PKII↓)	0
Poly(I)·poly(C) (PKR↑)§	0

Activity was assayed as in Fig. 1. Nuclear RNA was present at 100 μg/ml unless otherwise noted. 2,3-Bisphosphoglycerate was used at 6 and 12 mM; quercetin was used at 50 and 100 μM; H-7 was used at 10 μM; staurosporine was used at 2 and 5 nM; EGTA was used at 50 mM; and poly(I)·poly(C) was used at 100 μg/ml. 

^*In parentheses are indicated the known inhibitory or stimulatory effects on various kinases. CKII, casein kinase II; PKA, protein kinase A; PKC, protein kinase C; CaM-PKII, calmodulin-dependent protein kinase II; PKR, double-stranded RNA-activated protein kinase. 

^†Zero denotes no effect. 

^‡Staurosporine was initially thought to be a selective inhibitor of PKC (13, 14). Subsequent work (ref. 15, and references cited therein) has suggested that it is a preferential inhibitor of PKC, PKA, and certain of the cyclin-dependent kinases. Because staurosporine did not block the RNA-dependent phosphorylation of C1 hnRNP protein in the present investigation, the aforementioned caveats as to selectivity of action would, if anything, exclude even additional kinases. 

^§Poly(I)·poly(C) was used in place of nuclear RNA.