The evidence discussed in Chapters 1\u20133 indicates that in living organisms at least the primary control of gene expression lies at the level of transcription. However, in eukaryotes, several cases exist where changes in the rate of synthesis of a particular protein occur without a change in the transcription rate of the corresponding gene or where post-transcriptional controls operate as a significant supplement to transcriptional control. This indicates that in these cases regulatory processes are operating at the level of one or more of the post-transcriptional events, as described in Chapter 8. Indeed, in some lower organisms, post-transcriptional regulation may constitute the predominant form of regulation of gene expression.<\/p>\n\n\n\n