Viral pathogenesis and molecular biology.

Molecular biology applied toward understanding viral diseases has come of age. An exciting future is in store when questions of viral pathogenesis can be answered by biochemical analysis of animal viruses and their infected cells. This is not, however, a one-way street. Our experience has been that in designing experiments which attempt to answer questions related to disease processes new information is often gathered that contributes significantly to our thinking about general problems in molecular biology. This twoway exchange between molecular biology and viral pathogenesis will be illustrated here by recent examples in our work as well as in that of others. Studies on the structure of animal viruses have been most rewarding. Identification and separation of viral structural proteins have led to an understanding of the components on the virion surface that determine attachment and penetration into host cells. An example of the importance of these viral surface proteins is that of paramyxoviruses. For this group of viruses, the envelope is covered by glycoproteins that must be cleaved before the virus particle can become fully infectious (14, 51). This suggests that attachment and penetration of this virus into new tissues and new hosts may be determined by the presence or availability of specific proteases. A recent study positively correlates cleavage of the hemagglutinating and fusing proteins of Newcastle disease virus to its virulence for chickens (25).