Internal Components Released from Rhinovirus and Poliovirus by Heat

Abstract

Picornaviruses in general are quite heat-labile in the absence &cations (Wallis & Melnick, ~96z). McGregor & Mayor (~968) showed that heating purified preparations of poliovirus and rhinovirus at 5o ° for 2 min. led to the extrusion of ribonucleoprotein strands. These results suggested that gentle heating of the virus particles at slightly lower temperatures might offer a more easily controllable method of degradation.Suspensions of purified rhino-and poliovirus (o.I ml.) were heated at 45 ° or 5 o° for various periods. After heating, the preparations were cooled immediately in an ice bath and specimens were prepared for electron microscopy. Poliovirus (LsC) when heated at 45 ° for 3o to 6o sec. appeared to lose portions of its capsid structure leaving 'holes' in the particle (Fig. 2). A diffuse amorphous core resembling a 'puffball' was then released from within the capsid leaving an empty shell (Fig. 2). This component was not demonstrated previously by McGregor & Mayor 0968). Upon further heating the core became progressively extended, and after Io min. at 5 °0 only long strands and empty capsids were observed.In contrast, rhinovirus preparations were much more stable morphologically at 45 ° than poliovirus preparations. When heated for I rain. at 45 ° the majority of rhinovirus particles appeared to be still intact. Even when heating at 45 ° was continued up to Io min., only about half of the particles had released their RNA. Many of these empty particles were degraded into smaller subunits and individual capsomeres (Fig. 3). At 50o the degradation of the rhinovirus particles progressed rapidly. After 1 rain. few intact particles were found and many of the empty particles were degraded. As heating was continued up to lo rain., strands similar to those found with the poliovirus became progressively extended. The empty particles formed after the release of the virus RNA seemed to be very unstable and were generally degraded into smaller subunits. In an effort to slow down this process the volume of the virus suspension was increased to 0"5 ml. This material was then incubated at 50 ° for ~ min. followed by rapid cooling. Under these conditions results were obtained similar to those observed with poliovirus. Amorphous cores appeared to be released from within the capsids, leaving empty capsids which appeared, in addition, to have portions of their structure missing (Fig. 4). The material released from within the capsids was associated with partially extended strands.Samples at various stages of degradation were treated with specific enzymes in order to determine the chemical composition of the components (Table ~). When the cores were treated with RNase before extension occurred they seemed to be completely digested. Once extension occurred, however, the strands were completely resistant to digestion with RNase unless they were first treated with pepsin. These observations suggested that the virus RNA was first released from within the particle. This was followed by its unfolding and association with a protei...

Composition of poliovirus fibrils

“…(2) Their formation at pH 8 was reported to be inhibited by ribonuclease (5,6). Again, we were unable to reproduce this result (2, 13).…”

“…Of these, at least the poliovirus-derived fibrils are nucleoproteins, as the following findings show: (t) They were reported to be dissolved by pepsin ~ollowed by ribonucle~se (5,6). For some still unexplained reason, this was not so in our hands (2,13), and this discrepancy prompted the present reinvestigation.…”

“…The formation of fibrillar products as a result of disrupting the virion is a general property of the picornaviruses since it was observed with polio-, Echo-, Coxsaekie-and rhinoviruses (2,5,6,13). Of these, at least the poliovirus-derived fibrils are nucleoproteins, as the following findings show: (t) They were reported to be dissolved by pepsin ~ollowed by ribonucle~se (5,6).…”

“…Poliovirus and a variety of other picornaviruses yielded fibrils when disrupted by heat, alkaline pH, concentrated urea and other means (2,5,6,9,13). McGREGOR and MAYO~ (5,6) concluded that the fibrils of polio-and rhinovirus were ribonucleoproteins mainly on the strength of enzymic tests.…”

“…McGREGOR and MAYO~ (5,6) concluded that the fibrils of polio-and rhinovirus were ribonucleoproteins mainly on the strength of enzymic tests.…”