Structure and assembly of intracellular mature vaccinia virus: Thin-section analyses

In the preceding study (see accompanying paper), we showed by a variety of different techniques that intracellular mature vaccinia virus (vaccinia LNA is unexpectedly complex in its structural organization and that this compl exity also extends to the underlying viral core, which is highly folded. Wi th that analysis as a foundation, we now present different thin-section ele ctron microscopy approaches for analyzing the IMV and the processes by whic h it is assembled in infected HeLa cells. We focus on conventional epoxy re sin thin sections as well as cryosections to describe key intermediates in the assembly process. We took advantage of streptolysin O's ability to sele ctively permeabilize the plasma membrane of infected cells to improve membr ane contrast, and we used antibodies against bone fide integral membrane pr oteins of the virus to unequivocally identify membrane profiles in thin sec tions. All of the images presented here can be rationalized with respect to the model put forward for the assembly of the IMV in the accompanying pape r.