Immediate-early (IE) genes are the first class of viral genes expressed after 
primary infection or reactivation. As transcription of IE genes does not require 
prior viral protein synthesis, this class of genes is experimentally defined by 
their transcription following primary infection or reactivation in the presence 
of inhibitors of protein synthesis. This chapter describes an approach to 
identify IE genes in a novel herpesvirus genome. Transcription of IE genes is 
selectively induced with sodium butyrate in the presence of the protein 
synthesis inhibitor cycloheximide. The transcripts of the induced genes are 
identified by using a cDNA subtraction-based method of gene expression 
screening.