RESUMO
With routine procedures of Epon- or GMA-embedding and a stain specific for DNA, the nucleoid of mature herpes simplex virus-type 1 (HSV-1) assumes the well-known form of a short, compact, hollow cylinder or torus. A new, more complex organization of DNA filaments in encapsidated HSV-1 was found in infected cells after aldehyde fixation, methanol dehydration, and Lowicryl embedment. We have determined that it is the use of methanol as dehydrating agent that permits visualization of this internal structure. The same new spatial organization of DNA can be seen in Epon and GMA sections when methanol dehydration is used. This organization is lost in a methanol-ethanol sequence of dehydration but can be restored in an ethanol-methanol sequence. Dimethylsulfoxide (DMSO) is the only other agent among several reviewed here which resembles methanol in its effect on HSV-1 DNA. Methanol had the same effect on five subfamilies of the herpes group (HSV-1, HSV-2, CCV, CMV, CTHV) but did not alter the nucleoid ultrastructure in simian virus 40 (SV40) and adenovirus type 5 (Ad 5). Therefore, it may sometimes, but not always, provide additional information about the organization of biological structures.
