Early events in DNA packaging in a defined in vitro system of XXXX .

@entity56197 @entity1025 @entity855 @entity12865 @entity968
We have developed a defined in vitro system for packaging @entity56197 DNA which is composed of purified proheads and the noncapsid proteins gp18 and gp19, products of genes 18 and 19. The reaction requires @entity1025 , @entity855 , and @entity968 and is inhibited by a nonhydrolyzable @entity855 analog, @entity12865 ( @entity855 -gamma-S) (K. Hamada, H. Fujisawa, and T. Minagawa, 1986, Virology 151, 119-123). About 30% of added mature @entity56197 DNA was packaged into heads in the defined system. A complex with a sedimentation coefficient of about 50 S (50 S complex) accumulated in the reaction mixture containing @entity855 -gamma-S. The 50 S complex was DNase sensitive and was converted to filled heads by a second reaction in the presence of @entity855 without addition of DNA, proheads, gp18, and gp19. These results indicate that during early stages of DNA packaging, formation of precursor complexes proceeds by an allosteric mechanism with @entity855 acting as effector. The movement of DNA into the head is driven by the energy released by hydrolysis of @entity855 . gp18 formed a complex with DNA without addition of @entity855 -gamma-S and gp19. gp18-DNA complex was DNase sensitive and did not bind gp19; it was converted to filled heads by way of a second reaction after addition of @entity855 , gp19, and proheads. gp19 formed a functional complex with prohead in the presence of @entity855 -gamma-S or @entity855 . The complex did not bind gp18 but was converted to filled heads by incubation with @entity855 , gp18, and DNA. In the absence of @entity855 -gamma-S, gp19 formed complexes with prohead that were abortive in DNA packaging. Formation of the 50 S complex occurred in a reaction mixture containing gp18-DNA and gp19-prohead complexes in the presence of @entity855 -gamma-S. From these results, we propose details of the molecular mechanism of DNA packaging in the defined in vitro system.
