The double-stranded RNA dependent eIF-2 alpha kinase (PKR) has been im
plicated in the regulation of a number of cellular processes including
cell growth and differentiation. Previous studies using embryonic mou
se 3T3-F442A cells have indicated that PKR undergoes phosphorylation a
nd activation in vivo. This activation of PKR has been attributed to a
subset of poly(A)(+)-rich cellular RNA (R-RNA) having sufficient seco
ndary structure to interact with the kinase. To characterize the R-RNA
activity, a cDNA was prepared which, when transcribed in vitro, gave
rise to an RNA transcript that retained its property to activate PKR.
The ability of the transcript to activate PKR was sensitive to ribonuc
lease V1 and was abolished by the addition of high concentrations of p
oly(I).poly(C). The cloned cDNA was utilized for liquid RNA/DNA hybrid
ization experiments, which disrupted the secondary structure of the R-
RNA and for Northern blot analysis. The results from these studies ind
icated that the measurable RRNA activity was represented in a specific
cellular RNA which was responsible for the activation of PKR. Further
more it was found that the R-RNA was specifically associated with PKR
and that this complex could be detected directly in cell extracts. The
nucleotide sequence of the cDNA was determined. We propose that this
novel cellular RNA may play a critical role in regulating the activati
on of PKR and thus be an important component in the control of cell gr
owth and differentiation.