Abstract
BackgroundIn yeast, birds and mammals, the SAPK-interacting protein 1 (Sin1) gene product has been implicated as a component of the stress-activated protein kinase (SAPK) signal transduction pathway. Recently, Sin1 has also been shown to interact with the carboxyl terminal end of the cytoplasmic domain of the ovine type I interferon receptor subunit 2 (IFNAR2). However, the function of Sin1 remains unknown. Since SAPK pathways are ancient and the IFN system is confined to vertebrates, the organization of the Sin1 gene and the sequences of the Sin1 protein have been compared across a wide taxonomic range of species.ResultsSin1 is represented, apparently as a single gene, in all metazoan species and fungi but is not detectable in protozoa, prokaryotes, or plants. Sin1 is highly conserved in vertebrates (79–99% identity at amino acid level), which possess an interferon system, suggesting that it has been subjected to powerful evolutionary constraint that has limited its diversification.Sin1 possesses at least two unique sequences in its IFNAR2-interacting region that are not represented in insects and other invertebrates. Sequence alignment between vertebrates and insects revealed five Sin1 strongly conserved domains (SCDs I-V), but an analysis of any of these domains failed to identify known functional protein motifs. SCD III, which is approximately 129 amino acids in length, is particularly highly conserved and is present in all the species examined, suggesting a conserved function from fungi to mammals. The coding region of the vertebrate Sin1 gene encompasses 11 exon and 10 introns, while in C. elegans the gene consists of 10 exons and 9 introns organized distinctly from those of vertebrates. In yeast and insects, Sin1 is intronless.ConclusionsThe study reveals the phylogeny of a little studied gene which has recently been implicated in two important signal transduction pathways, one ancient (stress response), one relatively new (interferon signaling).
Highlights
In yeast, birds and mammals, the SAPK-interacting protein 1 (Sin1) gene product has been implicated as a component of the stress-activated protein kinase (SAPK) signal transduction pathway
The study reveals the phylogeny of a little studied gene which has recently been implicated in two important signal transduction pathways, one ancient, one relatively new
The marked dissimilarity in inferred amino acid sequence between Sin1 from vertebrates and C. elegans (25% identity, Table 2), between the two yeast species (29% identity, Table 2; see Additional file: 1) and between S. pombe and N. crassa (28% identity, Table 2, see Additional file: 2) in the approximately 500 aa of overlap suggests that even if homologs existed in plants and prokaryotes they would likely be overlooked by the search methods employed
Summary
Birds and mammals, the SAPK-interacting protein 1 (Sin1) gene product has been implicated as a component of the stress-activated protein kinase (SAPK) signal transduction pathway. RAS2Val 19 mutation had elevated levels of cyclic AMP, impaired growth control and were acutely sensitive to heat shock This phenotype was reversed when the yeast strain was transfected with a cDNA (clone JC310) that encoded a unknown protein. Eight years after the identification of JC310 it was again identified, on this occasion in a yeast twohybrid screen of a Schizosaccharomyces pombe cDNA library as a 665 amino acid protein that bound via polypeptide sequences in its C-terminal 244 amino acids to the Sty1/ Spc, stress activated MAP kinase (SAPK) [2]. Fusion of the first 486 amino acids of yeast Sin (which does not restore growth) with the C-terminal 182 amino acids of the chicken Sin sequence protected against heat shock Together, these data showed that Sin functions as a component of the stress-activated Sty1/Spc MAP kinase pathway in S. pombe and that a functional homolog of Sin exists in vertebrates
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