title: RAP2B: a RAS-related GTP-binding protein from platelets.
abstract: A platelet cDNA expression library was screened with the monoclonal antibody M90, which recognizes a specific epitope on RAS-encoded p21 proteins (amino acids 107-130). DNA sequence analysis of one clone revealed that it encoded a partial amino acid sequence of a protein closely related to RAP2, which we have named RAP2B. A repeated screening of the platelet cDNA library with an internal Ava I fragment of the RAP2B cDNA allowed the isolation of a full-length cDNA for the RAP2B sequence. RAP2B is 90% identical to RAP2 at the amino acid level with the most variability at the carboxyl terminus of the protein. Oligonucleotides were synthesized to complete the amino acid sequence of the RAP2B protein and the entire sequence was expressed in Escherichia coli. Analysis of crude soluble extracts indicated that RAP2B was a Mr 22,000 protein that specifically bound GTP on blots. Moreover, incubation of similar extracts with the catalytic subunit of cAMP-dependent protein kinase did not cause phosphorylation of RAP2B, as had been observed for the closely homologous proteins, RAP1A and RAP1B. These results suggest that RAP2B, like the other RAP proteins, is a low molecular weight GTP-binding protein in human platelets.
authors.affiliation: Division of Cell Biology, Burroughs Wellcome Co., Research Triangle Park, NC 27709.
authors.forename: C A
authors.initials: CA
authors.lastname: Ohmstede
authors.forename: F X
authors.initials: FX
authors.lastname: Farrell
authors.forename: B R
authors.initials: BR
authors.lastname: Reep
authors.forename: K J
authors.initials: KJ
authors.lastname: Clemetson
authors.forename: E G
authors.initials: EG
authors.lastname: Lapetina
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001792:Blood Platelets / Q000378:metabolism*; D003001:Cloning, Molecular; D019204:GTP-Binding Proteins / Q000097:blood / Q000235:genetics* / Q000302:isolation & purification; D015723:Gene Library; D011905:Genes, ras; D006801:Humans; D008969:Molecular Sequence Data; D008970:Molecular Weight; D015345:Oligonucleotide Probes; D011494:Protein Kinases / Q000378:metabolism; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D020668:rap GTP-Binding Proteins
chemical_list: D015345:Oligonucleotide Probes; D011494:Protein Kinases; D019204:GTP-Binding Proteins; C065562:RAP2B protein, human; D020668:rap GTP-Binding Proteins