title: p619, a giant protein related to the chromosome condensation regulator RCC1, stimulates guanine nucleotide exchange on ARF1 and Rab proteins.
abstract: We report the identification of a novel human gene, designated p619, that encodes a polypeptide of 4861 amino acid residues, one of the largest human proteins known to date. The p619 protein contains two regions of seven internal repeats highly related to the cell cycle regulator RCC1, a guanine nucleotide exchange factor for the small GTP binding protein, Ran. In addition, p619 possesses seven beta-repeat domains characteristic of the beta-subunit of heterotrimeric G proteins, three putative SH3 binding sites, seven polar amino acid-rich regions, a putative leucine zipper and a carboxy-terminal HECT domain characteristic of E3 ubiquitin-protein ligases. p619 is expressed ubiquitously in mouse and human tissues and overexpressed in several human tumor cell lines. Subcellular localization studies indicate that p619 is located in the cytosol and in the Golgi apparatus. Localization of p619 in the Golgi is altered by Brefeldin A. The carboxy-terminal RCC1-like domain of p619 interacts specifically with myristoylated ARF1, a small GTP binding protein also located in the Golgi. Moreover, the second RCC1-like motif located at the amino-terminus of p619 stimulates guanine nucleotide exchange on ARF1 and on members of the related Rab proteins, but not on other small GTP binding proteins such as Ran or R-Ras2/TC21. These observations suggest that p619 is a Brefeldin A-sensitive Golgi protein that functions as a guanine nucleotide exchange factor for ARF1 and, possibly, for members of the Rab family of proteins.
authors.affiliation: Department of Molecular Oncology, Bristol-Myers Squibb, Pharmaceutical Research Institute, Princeton, NJ 08543, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Rosa
authors.forename: R P
authors.initials: RP
authors.lastname: Casaroli-Marano
authors.forename: A J
authors.initials: AJ
authors.lastname: Buckler
authors.forename: S
authors.initials: S
authors.lastname: Vilaró
authors.forename: M
authors.initials: M
authors.lastname: Barbacid
mesh_terms: D020823:ADP-Ribosylation Factor 1; D020727:ADP-Ribosylation Factors; D000595:Amino Acid Sequence; D000818:Animals; D020126:Brefeldin A; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D003001:Cloning, Molecular; D003517:Cyclopentanes / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000737:chemistry*; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism* / Q000502:physiology*; D005796:Genes; D006056:Golgi Apparatus / Q000378:metabolism; D020730:Guanine Nucleotide Dissociation Inhibitors; D020662:Guanine Nucleotide Exchange Factors; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009183:Mycotoxins / Q000494:pharmacology; D009687:Nuclear Proteins; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D012091:Repetitive Sequences, Nucleic Acid; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases
chemical_list: D018797:Cell Cycle Proteins; D003517:Cyclopentanes; D004268:DNA-Binding Proteins; C086796:GDP dissociation inhibitor 1; D020730:Guanine Nucleotide Dissociation Inhibitors; D020662:Guanine Nucleotide Exchange Factors; D009183:Mycotoxins; D009687:Nuclear Proteins; C062521:RCC1 protein, human; D012333:RNA, Messenger; C499302:Rcc1 protein, mouse; D020126:Brefeldin A; D006160:Guanosine Triphosphate; C102169:HERC1 protein, human; D044767:Ubiquitin-Protein Ligases; D019204:GTP-Binding Proteins; D020823:ADP-Ribosylation Factor 1; D020727:ADP-Ribosylation Factors