SR proteins

Neugebauer K.M., Merrill J.T., Wener M.H., Lahita R.G., and Roth M.B. (2000), SR proteins are autoantigens in patients with systemic lupus erythematosus. Importance of phosphoepitopes, Arthritis Rheum. 43, 1768-1778. 

The composition of the spliceosome determines the pattern of chosen sphce sites. Several proteins have been identified which act as antagoiusts in the selection of sphce sites. The SF2 protein (and related proteins) belong to the family of SR proteins (SR Ser- and Arg-rich) and supports the use of 5 -sphce sites. Another protein, the hnRNP A1 protein supports the use of 3 -splice sites. 

Alternative splicing could have arisen accidentally, but it is controlled by proteins. Best known is the alternative splicing factor (ASF or SF2).612,637 It was first recognized by its function in Drosophila melano-gaster, where the sex of individuals is determined by alternative splicing of an mRNA.638 In addition to ASF other serine- and arginine-rich SR proteins participate in alternative splice site selection.612... 

Zhong, Y., Ahmed, S., Grupp, I. L., and Matlib, M. A. (2001). Altered SR Protein Expression Associated with Contractile Dysfunction in Diabetic Rat Hearts. Am J Physiol Heart Circ Physiol 281(3) HI 137 17. 

Valcarcel, J. and Green, M.R. (1996) The SR protein family pleiotropic functions in pre-mRNA splicing. Trends Biochem. Sci. 21, 296-301. 

Fig. 1 Representative splicing cu-elements and tran -factors. Tissue-specific and developmental stage-specific expressions of splicing trans-factors including SR proteins and hnRNP Al enable precise regulations of alternative splicing. ISE and ISS have similar activities as ESE and ESS, but are omitted firom the figure...

Tacke, R., Manley, J.L. (1999). Determinants of SR protein specificity. Curr. Opin. Cell. Biol. 11 358-62. 

As in the SR protein family (serine- and arginine-rich proteins) also sarcoplasmic reticnlnm, scavenger receptor Synchrotron radiation circnlar dichroism Semm response factor, a nbiqnitons transcription factor Signal recognition particle SR protein kinase... 

Component of the spliceosome, the intron-removing apparatus in eukaryotic nuclei. See Graveley, B.R., Sorting out the complexity of SR protein fnnctions, RNA 6, 1197-1211, 2000 Will, C.L. and Luhrmann, R., Spliceosomal UsnRNP biogenesis, strnctnre, and function, Curr. Opin. Cell Biol. 13, 290-301, 2001 Turner, LA., Norman, C.R., Chnrcher, M.J., and Newman, A.J., Roles of the U5 snRNP in spliceosome dyanamics and catalysis, Biochem. Soc. Trans. 32, 928-931, 2004. 

Figure 4.1.5 In vitro effects of triorganotin compounds on rat cardiac SR protein phosphorylation. (Reproduced from Reference 41, with kind permission of Springer Science and Business Media.)...

Both methods involve swelling of the cells in hypotonic solution, disruption of the plasma membrane, and extraction of the nuclei in a high salt buffer. The extracts support a number of nuclear functions and have been extremely useful in studying transcription and splicing (see Section 5.1). Nuclear extracts are also a useful starting point for purification of snRNAs, snRNPs, hnRNP proteins and SR-proteins (Section 3.1.2). 

Transfer the resuspended pellet containing the purified SR proteins to a fresh tube. 

Check purity of SR-proteins by SDS-PAGE gel electrophoresis either followed by Coomassie staining or by immunoblotting using mAb 104 antibody.0... 

SR-proteins can be expressed as recombinant proteins in Escherichia coli, but they lack the post-translational phosphorylation of the serine residues and are poorly soluble in the absence of chaotropic reagents. It is possible to phosphorylate bacterially produced protein by preincubation in nuclear extract or, even more efficiently, by the addition of purified recombinant SR-protein specific kinases Clk/Sty8 or SRPK.9 Soluble and phosporylated SR-proteins can also be produced in insect cells using the baculovirus system10 although it is not resolved whether these proteins behave exactly as those produced in human cells. 

Chromatographic purification of individual SR-proteins is difficult due to their structural similarity. A SDS gel purification procedure involving a renaturation step has been published.11... 

Splicing is facilitated by splicosomes that consist of more than 100 proteins and five small nuclear (sn) RNAs (snRNAs). Certain regulatory proteins called splicing regulator (SR) proteins bind to a particular nucleotide sequence in the exon called the exon splicing enhancer (ESE) and recruit splicosomes. The exon may contain an exon splicing suppressor (ESS) sequence, which prevents the splicosome from splicing. 

SR Proteins Contribute to Exon Definition in Long Pre-mRNAs... 

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