A hnRNP is............?

a) a RNA-protein complex formed prior to export from the nucleus

b) a DNA-RNA hybrid duplex created during transcription

c) a RNA-protein complex which assists translation of other proteins

d) a RNA-protein complex that is transcribed but not translated

e) a RNA-protein complex translated by the ribosome
a) an RNA-protein complex formed prior to export from the nucleus.



In reality, mRNA is never found either in the nucleoplasm or the cytoplasm unless it is complexed with proteins. This RNA-protein complex is called hnRNP which is an abreviation for heterogeneous nuclear ribonucleoprotein. Any piece of RNA that is found in the nucleus or cytoplasm not attached to certain proteins are highly susceptible to degradation by exonucleases, enzymes specifically present to degrade RNA.
well scientists identified the gene smooth (sm) in a screen for genes that are specifically expressed within the lineage that forms the adult chemosensory bristles. sm is expressed in most or all differentiating neurones during embryogenesis, but is specifically expressed in the neurones of the adult chemosensory organs on the wings and legs during metamorphosis. The inactivation of sm results in axonal defects in the chemosensory neurones, in the inability of mutant flies to feed and in their precocious death. As sm belongs to a family of heterogeneous nuclear ribonucleoprotein (hnRNP), we propose that the control of axonal navigation and connectivity is partly achieved at the level of mRNA splicing or exporting.



The Scientists Conclusion

scientists analysed the pattern of expression of sm by in situ hybridization throughout development. sm is not expressed until late stages of embryogenesis, when transcripts are observed in most or all neurones of the CNS and in a subset of chordotonal neurones as well as, at a lower level, in other sensory neurones. No other tissue or structure is labelled during embryogenesis.