Alpha 2-chimerin, an SH2-containing GTPase-activating protein for the ras-related protein p21rac derived by alternate splicing of the human n-chimerin gene, is selectively expressed in brain regions and testes.
n-Chimerin (alpha 1-chimerin) is a brain GTPase-activating protein (GAP) for the ras-related p21rac. We now report the occurrence of another form of chimerin, termed alpha 2-chimerin. This is the product of an alternately spliced transcript of the human n-chimerin gene encoding an N-terminal SH2 (src homology 2) domain in addition to the phorbol ester receptor and GAP domains. alpha 1- and alpha 2-chimerin mRNAs were expressed differently. In the rat brain, only alpha 1-chimerin mRNA was expressed in cerebellar Purkinje cells, although both alpha 1- and alpha 2-chimerin mRNAs occurred in neurons in the cerebral cortex, hippocampus, and thalamus. Only alpha 2-chimerin RNA was expressed in rat testes, in early pachytene spermatocytes. A 45-kDa SH2-containing chimerin corresponding to the alpha 2 form was purified from rat brain. As with Escherichia coli 45-kDa recombinant alpha 2-chimerin, purified brain alpha 2-chimerin exhibited racGAP activity which was stimulated by phosphatidylserine. The recombinant SH2 domain bound several 32P-labelled phosphoproteins of PC12 cells, whose phosphorylation increased in response to trophic factors, including nerve growth factor. To examine the relationships of alpha 1- and alpha 2-chimerin transcripts, human genomic DNA clones were characterized. In alpha 2-chimerin mRNA, a 3' splice acceptor site within exon 1 of alpha 1-chimerin mRNA was used, replacing its 5' untranslated region and N-terminal coding sequence. The single human n-chimerin gene was mapped to chromosome 2q31-q32.1, colocalizing with the CRE-BP1 transcription factor gene (2q32). It contained several splice junctions conserved with the sequence-related protein kinase C and bcr genes. alpha 2-Chimerin is only the second SH2-containing GAP and the first example of an SH2 domain generated by alternate splicing.
Hall
C
C
Department of Neurochemistry, Institute of Neurology, London.
Sin
W C
WC
Teo
M
M
Michael
G J
GJ
Smith
P
P
Dong
J M
JM
Lim
H H
HH
Manser
E
E
Spurr
N K
NK
Jones
T A
TA
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000378:metabolism; D020848:Chimerin 1; D002889:Chromosomes, Human, Pair 2; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D005091:Exons; D019204:GTP-Binding Proteins / Q000378:metabolism; D020690:GTPase-Activating Proteins; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics*; D016716:PC12 Cells; D010718:Phosphatidylserines / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D011493:Protein Kinase C / Q000235:genetics; D011505:Protein-Tyrosine Kinases; D011506:Proteins / Q000235:genetics*; D011518:Proto-Oncogene Proteins / Q000235:genetics; D051562:Proto-Oncogene Proteins c-bcr; D015183:Restriction Mapping; D016415:Sequence Alignment; D013090:Spermatocytes / Q000378:metabolism; D013737:Testis / Q000378:metabolism; D020744:rac GTP-Binding Proteins; D020703:ras GTPase-Activating Proteins
D020848:Chimerin 1; D020690:GTPase-Activating Proteins; D009419:Nerve Tissue Proteins; D010718:Phosphatidylserines; D010750:Phosphoproteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D020703:ras GTPase-Activating Proteins; D004247:DNA; D011505:Protein-Tyrosine Kinases; C496613:BCR protein, human; D051562:Proto-Oncogene Proteins c-bcr; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D020744:rac GTP-Binding Proteins