Genome expression and replication

The majority of viruses express their genetic information in successive phases, such that the transcription of early and late genes gives rise to a range of proteins both before (early) and after (late) genome replication has begun. As we have described,

Figure:  Herpes simplex  virus replication. The replication stages represented are attachment (a), penetration (b), trafficking (c), uncoating (d), early gene transcription (e), genome replication (f), late gene transcription (g), capsid assembly (h), and virus egress (i).

   Figure:  Human  papillomavirus replication. The replication stages represented (a–h) are as for above figure

           Figure:   Poliovirus replication. The replication stages represented (a–h) are as for Figure

              Figure:   Influenza virus replication. The replication stages represented (a–i) are as for Figure

             Figure:  HIV replication. The replication stages represented (a–i) are as for Figure .

late  virus  gene  expression is dependent on  the  prior synthesis of early  proteins (both immediate early and  delayed early) but it is important to grasp that for many viruses, the initiation of early gene  expression itself relies  on viral proteins that are enclosed within the  virion  and  some of these are  late  proteins synthesized during replication within a previously infected cell. In addition, viruses also make use of cellular proteins, especially during early gene expression, before cell protein synthesis is shut off. The range and com- plexity of genome expression and replication strategies are very large, and to illustrate this we will consider the five viruses selected individually.