Isolation and replication of an occlusion body-deficient mutant of the Autographa californica nuclear polyhedrosis virus

Abstract

A spontaneous mutant of the Autographa californica nuclear polyhedrosis virus which was deficient in viral occlusion body formation was studied in Trichoplusia ni tissue culture cells. Virus multiplication could be divided into four phases based on growth curves and the sequential appearance of 25 viral-induced proteins identified by pulse labeling and polyacrylamide gel electrophoresis. During the latent phase, five viral-induced proteins with molecular weights of 68, 47, 35, and 30 thousand (K) were detected. The synthesis of 17 additional viral-induced proteins with molecular weights ranging from 64 to 14K was detected during the nonoccluded virus (NOV) phase, 10 to 16 hr postinoculation (pi). During the transition from NOV to occluded virus formation, 16 to 34 hr pi, the synthesis of occlusion body matrix protein (33K) and two additional proteins (15.6 and 13K) was detected. During the occlusion phase of replication, after 34 hr pi, NOV synthesis ceased; however, the synthesis of the 25 viral-induced proteins continued. Posttranslational cleavage was not detected in pulse-chase experiments. The occlusion body-deficient mutant induced lower levels of occlusion body matrix protein synthesis than the wild type virus. The decrease in amount of occluded virions was accompanied by a corresponding increase in the number of NOV particles produced.