ISSN:
1573-4978
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract In this report we describe some recent and, in some cases, preliminary results on the characterization of messenger ribonucleoprotein complexes isolated from the nucleus and various subcellular compartments of immature avian red blood cells. Reviewing investigations carried out over the last ten years, we try to draw some general conclusions regarding the composition and significance of the protein associated with pre-mRNA in the nucleus and with translated and untranslated mRNA in the cytoplasm. Furthermore, we propose a flow diagram through the cell of the various consecutive carriers of genetic information. In the case of nuclear RNP the main conclusions for our research are that pre-mRNA is associated with a relatively small group of approximately 20 basic proteins which may be involved in structural functions, and with a larger population estimated to contain at least 60 acidic polypeptides. This latter group has the theoretical characteristics of agents involved in post-transcriptional regulation, analogous to the putative role of non-histone proteins in transcription. The proteins of translated mRNP complexes are associated with specific segments of the mRNA; their function is unclear since they neither inhibit nor stimulate translation of their endogenous mRNA. However, in addition there exists genuinely repressed mRNA in the terminally differentiated erythroblast since the mRNA population in polyribosomes contains ten times fewer messages than the ribosome-free mRNP complexes. Of the order of 25% of the cytoplasmic globin mRNA is found in the untranslated fraction; thisin vivo repressed globin mRNP is also untranslatablein vitro, unless it is fully deproteinized. Since different messages in the untranslated mRNP compartment are associated with different sets of proteins we suppose that specific mRNAs can be recognized by specific sets of proteins in low redundancy, and can be drawn into the repressed state. We conclude that it is probable that RNP proteins play some role in post-transcriptional regulation of gene expression.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00777487
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