Previous studies indicate that
RNA may be required for
proteinase-resistant
prion protein (PrP) amplification and for infectious
prion formation in vitro, suggesting that
RNA molecules may function as cellular cofactors for abnormal PrP (PrPSc) formation and become part of the structure of the infectious agent. To address this question, we used chemicals that can cleave phosphodiester bonds of
RNA and assessed their effects on the infectious agent.
Lithium aluminum hydride, a
reducing agent that can induce reductive cleavage of oxidized molecules such as carbonyls, carboxyl
acids,
esters, and phosphodiester bonds, did not affect cellular PrP degradation; however, it destroyed PrPSc, extended the
scrapie incubation period, and markedly reduced total
RNA concentrations. These results prompted us to investigate whether
RNA molecules are cofactors for PrPSc propagation.
RNase A treatment of partially purified PrP and of 263K
scrapie brain homogenates was sufficient to increase the sensitivity of PrPSc to
proteinase K degradation. This is the first evidence that suggests that
RNA molecules are a component of PrPSc. Treatment with
RNase A alone and PrP degradation by
RNase A plus
proteinase K in vitro, however, did not result in loss of
scrapie infectivity compared with the effects of
lithium aluminum hydride. Together, these data suggest that
RNA molecules may be important for maintaining the structure of PrPSc and that oxidized molecules can be important in
scrapie agent replication and
prion infectivity.