Variety in the level of gene control in eukaryotic cells.

In light of present progress in the understanding of how messenger RNA is constructed in eukaryotic cells, the levels of gene control are discussed. Transcriptional control, assessed by the rate of synthesis of specific nuclear RNA, is strongly indicated to be the most frequent level of control. Definition of eukaryotic transcription units as simple (encoding one protein) and complex (encoding two or more proteins) affords a framework in which to discuss control at the level of RNA processing for which several examples also are known. Finally, differential stability of cytoplasmic mRNAs and differential translation, both well established, are briefly described.