Transperons: RNA operons as effectors of coordinated gene expression in eukaryotes

Coordinated gene expression allows spatiotemporal control of cellular processes and is achieved by the cotranscription/translation of functionally related genes/proteins. Prokaryotes evolved polycistronic messages (operons) to confer expression from a single promoter to efficiently cotranslate proteins functioning on the same pathway. Yet, despite having far greater diversity (e.g., gene number, distribution, modes of expression), eukaryotic cells employ individual promoters and monocistronic messages. Although gene expression is modular, it does not account for how eukaryotes achieve coordinated localized translation. The RNA operon theory states that mRNAs derived from different chromosomes assemble into ribonucleoprotein particles (RNPs) that act as functional operons to generate protein cohorts upon cotranslation. Work in yeast has now validated this theory and shown that intergenic associations and noncanonical histone functions create pathway-specific RNA operons (transperons) that regulate cell physiology. Herein the involvement of chromatin organization in transperon formation and programmed gene coexpression is discussed.