The alternative translation of synaptotagmin 1 mediates the non-classical release of FGF1.

Although the extravesicular p40 domain of the transmembrane protein, p65 synaptotagmin (Syt) 1, is essential for the non-classical export of the signal peptide-less structure, FGF1, it was not possible to identify a specific intracellular protease responsible for the processing of p65 Syt1. Surprisingly, analysis of the p65 Syt1 coding sequence revealed the presence of two potential alternative ATG codons corresponding to Met103 and Met113 both of which were flanked by Kozak sequences. Indeed, in vitro translation of a Met103Ile but not a Met113Ile p65 Syt1 point mutant exhibited reduced expression of p40 Syt1 and the double p65 Syt1 Met103Ile and Met113Ile point mutant was unable to translate the p40 Syt1 isoform. Since the expression of the p65 Syt1 double point mutant inhibited the stress-induced release of FGF1, it is likely that the alternative translation of the p65 Syt1 transcript at Met103 may be involved in the generation of intracellular p40 Syt1, a critical component of the FGF1 release pathway.

A Tetrahymena orthologue of the mouse chaperonin subunit CCT gamma and its coexpression with tubulin during cilia recovery.

A Tetrahymena pyriformis gene orthologue to the mouse CCT gamma gene has been cloned and sequenced. The coding region of this gene, named TpCCT gamma, is interrupted by six introns and codes for a protein of 559 amino acid residues. This protein shares a 57.6% identity with the mouse CCT gamma protein whereas in average a 30% identity was found with CCT alpha proteins from mammalian to yeast. The expression of this gene was investigated by Northern blot hybridization in Tetrahymena exponentially growing cells and cells during cilia recovery. The TpCCT gamma gene is expressed producing a unique transcript of 2.1 kilobases. A relevant aspect of our findings is the coordinated response of TpCCT gamma and tubulin genes to cilia regeneration. TpCCT gamma and tubulin transcripts reached higher levels between 45-120 min of reciliation compared to those found in exponentially growing cells. These high levels could be the result of the increase in apparent transcription rates detected at 60 min of reciliation. We also observed that TpCCT gamma transcripts are not increased after exposure of Tetrahymena cells to a heat-shock (28-->34 degrees C). Our results seem to indicate an important role of this gene in the differentiation process of ciliogenesis.