mRNA transport from the nucleus to the cytoplasm is an essential step of eukaryotic gene expression. A pre-mRNA molecule undergoes modification, such as 5'-capping, splicing, and 3'-end processing, in the nucleus. The molecule being modified interacts with a large number of proteins and, thus, mRNP particles are formed. The binding of factors involved in nuclear export also occurs during transcription and mRNA processing. We have shown that the functioning of TREX-2, an mRNA export complex, is restricted to the nucleus. We used the method of RNA coprecipitation that enables the selective extraction of RNA-protein complexes from samples to show that the transcription elongation complex TREX interacts with mRNA of the β-tubulin 56D gene over the entire length of the molecule. The capping protein Cbp80 reacted both with the cap structure and with a specific part of the coding mRNA of the β-tubulin 56D gene. The TREX-2 complex that mediates mRNA export from the nucleus to the cytoplasm is bound to the same part of the coding sequence. Thus, we identified a common binding site for all of the complexes under investigation on the mRNA of β-tubulin 56D. Co-immunoprecipitation reactions performed with S2 cell extracts revealed interactions between the components of complexes involved in transcription elongation, maturation, and export of mRNA. The model of molecular folding for the mRNP particle involving the mRNA of β-tubulin 56D has been proposed.
Keywords: RNP particle; TREX; TREX-2; mRNA export.