ENZYMATIC VARIANTS OF INFLUENZA VIRUS III

Padgett, Billie L. (University of Wisconsin, Madison), and Duard L. Walker. Enzymatic variants of influenza virus. III. Function of neuraminidase in the viral growth cycle. J. Bacteriol. 87:363–369. 1964.—Multiplication of a slowly reacting enzymatic variant of influenza B virus, strain LEE, was compared with that of parent virus in ovo. At 35 C, although their final yields were equal, variant virus reached its peak concentration in the allantoic fluids later than parent virus. At 39 C, multiplication of both viruses was slower, parent virus requiring 4 hr and variant virus 8 hr longer to reach infectivity levels comparable with those at 24 hr at 35 C. Variant enzyme activity in vitro can be controlled by altering the temperature and calcium concentration. Growth curves of these viruses in pieces of chorioallantoic membrane (CAM) in culture under conditions in which the variant should be as active as the parent revealed only minor differences between them. Under conditions in which variant enzyme activity would be much slower than the parent, the release of variant virus from the CAM was delayed and the rate of release was slower. Under the most adverse conditions, 39 C and no calcium, formation of infectious variant virus ceased after 5 hr, and the hemagglutination inhibitor in the cells was not degraded although hemagglutinins were produced. These findings are discussed in relation to the function of neuraminidase during viral multiplication.