The process of removing sections of the primary RNA transcript to remove sequences not present in the mature form of the RNA and joining the remaining sections to form the mature form of the RNA.
During the screening of a human placenta cDNA library, realized in order to isolate the P2Y(11) coding sequence, an unrelated cDNA was cloned. We identified a 1422 bp open reading frame encoding a human protein displaying 40% amino acid identity with the Saccharomyces cerevisiae Ssf-1, a protein involved in the second step of mRNA splicing. Sequencing of the corresponding genomic DNA showed that the gene encoding human Ssf-1 is located upstream to the P2Y(11) gene on chromosome 19p31. Comparison of the cDNA and genomic DNA sequences revealed that the human Ssf-1 gene is split into 12 exons. Northern blotting experiments showed that the 1.7 kb Ssf-1 mRNA presents an ubiquitous tissue expression. We also show that, in HL-60 human promyelocytic leukemia cells, Ssf-1 mRNA is rapidly upregulated following a treatment by granulocyte-colony stimulating factor and dibutyryl-cyclicAMP, two agents known to induce the granulocytic differentiation of these cells.
A chimeric transcript, characterized by the first third of PPAN exon 12 joined to P2RY11 exon 2, has been detected. It is possibly produced by trans-splicing. The chimeric transcript is widely expressed and can be induced by retinoic acid during the granulocytic differentiation of the HL60 cell line. The resulting chimeric protein shows a much lower activity than the non-chimeric P2RY11 gene product, but qualitatively indistinguishable (PubMed11278528).
The P2Y(11) receptor is an ATP receptor positively coupled to the cAMP and phosphoinositide pathways. Ssf1 is a Saccharomyces cerevisiae nuclear protein, which plays an important role in mating. The gene encoding the human orthologue of SSF1 is adjacent to the P2Y(11) gene on chromosome 19. During the screening of placenta cDNA libraries, we isolated a chimeric clone resulting from the intergenic splicing between the P2Y(11) and SSF1 genes. The fusion protein was stably expressed in CHO-K1 cells where it generated a cAMP response to ATP qualitatively indistinguishable from that of the P2Y(11) receptor. According to both Western blotting and cAMP response, the expression of the fusion protein in the transfected cells was clearly lower than that of the P2Y(11) receptor. Both P2Y(11) and SSF1 probes detected a 5.6-kb messenger RNA with a similar pattern of intensity in each of 11 human tissues. The ubiquitous presence of chimeric transcripts and their up-regulation during granulocytic differentiation indicate that the transgenic splicing between the P2Y(11) and the SSF1 genes is a common and regulated phenomenon. There are very few examples of intergenic splicing in mammalian cells, and this is the first case involving a G-protein-coupled receptor.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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