Rin, a neuron-specific and calmodulin-binding small G-protein, and Rit define a novel subfamily of ras proteins.
cDNAs encoding two novel 25 kDa Ras-like proteins, Rit and Rin, were isolated from mouse retina using a degenerate PCR-based cloning strategy. Using the expressed sequence tag database, human orthologs were also obtained and sequenced. The protein sequences of Rit and Rin, which are 64% identical, are more similar to each other than to any known Ras protein. Their closest homologs in the databases are Mucor racemosus Ras2 and Ras3, to which they show approximately 48% identity. Rit and Rin both bind GTP in vitro. An unusual feature of their structure is that they lack a known recognition signal for C-terminal lipidation, a modification that is generally necessary for plasma membrane association among the Ras subfamily of proteins. Nonetheless, transiently expressed Rit and Rin are plasma membrane-localized. Both proteins contain a C-terminal cluster of basic amino acids, which could provide a mechanism for membrane association. Deletion analysis suggested that this region is important for Rit membrane binding but is not necessary for Rin. Rit, like most Ras-related proteins, is ubiquitously expressed. Rin, however, is unusual in that it is expressed only in neurons. In addition, Rin binds calmodulin through a C-terminal binding motif. These results suggest that Rit and Rin define a novel subfamily of Ras-related proteins, perhaps using a new mechanism of membrane association, and that Rin may be involved in calcium-mediated signaling within neurons.
Lee
C H
CH
Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-9289, USA.
Della
N G
NG
Chew
C E
CE
Zack
D J
DJ
D000818:Animals; D002118:Calcium / Q000502:physiology; D002148:Calmodulin-Binding Proteins / Q000502:physiology*; D003001:Cloning, Molecular; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D019204:GTP-Binding Proteins / Q000502:physiology*; D015870:Gene Expression / Q000502:physiology; D006023:Glycoproteins / Q000235:genetics* / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D017403:In Situ Hybridization; D008565:Membrane Proteins / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D009474:Neurons / Q000737:chemistry* / Q000502:physiology; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000502:physiology; D012160:Retina / Q000737:chemistry / Q000166:cytology; D012680:Sensitivity and Specificity; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000235:genetics; D018631:ras Proteins / Q000145:classification* / Q000235:genetics* / Q000378:metabolism
D002148:Calmodulin-Binding Proteins; D017931:DNA Primers; D018076:DNA, Complementary; D006023:Glycoproteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C089283:Rit2 protein, mouse; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; C486776:RIT1 protein, human; C472865:Rit1 protein, mouse; D020559:Monomeric GTP-Binding Proteins; D018631:ras Proteins; D002118:Calcium