The mRNA-protein complexes (mRNPs, Messenger ribonucleoprotein particles) are the "couriers" of the modern eukaryotes that process, store and deliver messages (transcripts) from the nucleus to the appropriate subcellular compartments and beyond. Presence of mRNPs arbitrates the posttranscriptional control of gene expression by editing the precursor RNA to maturity, postulate its subcellular localization and/or storage and dictate its fate once in the cytoplasm; either to be translated or dispensed through mRNA degradation. Initiation of transcription is coupled with processing of the transcribed message and the immediate association of the transcript with a set of structural and regulatory proteins. Per se, mRNP complexes sub-optimize transcription by recruiting RNA-binding proteins which are the core component of the RNP activities that culminate overall distribution and abundance of individual proteins. This asymmetric distribution of the mRNA is the determinant of protein gradient and is known to influence cell polarity, cell fate and overall patterning during development. Embryo patterning in Drosophila, polarization of maternal mRNA to daughter cell in budding yeast and directional growth of mammalian neural cell and pollen tubes of flowering plants, are the most prominent examples of mRNP facilitated posttranscriptional control, influencing cell fates and patterns of development.This chapter addresses the current knowledge on the mechanisms of posttranscriptional control reinforced by the formation of RNP particles and reviews differences in the underlying mechanisms. The outline of the chapter encompasses step-wise cellular processes leading to the formation of mRNPs and its implication to cellular activities. A dedicated section is also integrated discussing the recent findings on the unique mechanism of RNP formation in the male gametophyte of Nicotiana tabaccum. A proposed model outlines the network of posttranscriptional control with a focus on the role of RNPs is also presented aiming to stimulate future research with a perspective of advancing our knowledge on the subject and its plausible application in improving food quality.

Institute of Experimental Botany AS CR Rozvojová Czech Republic

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