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rRNA-processing protein UTP23 homolog (UTP23) is a small subunit (SSU) processome component. The SSU processome is a complex involved in ribosome biogenesis and essential for pre-18S rRNA maturation. UTP23 is vital for the first 3 cleavage steps in 18S rRNA maturation. Furthermore, single-point mutations in the conserved putative active site of Utp24 but not Utp23 annul its function in ribosome biogenesis.

RNA binding motif protein 17 (RBM17) is a splice factor which binds to the single stranded 3'AG at the exon/intron border and promotes its utilization in the 2nd catalytic step. The RBM17 protein is involved in the regulation of alternative splicing and the utilization of cryptic splice sites. RBM17 protein also stimulates the utilization of a cryptic splice site created by the beta-110 mutation in the HBB gene. The ensuing frameshift leads to sickle cell anemia.

Rho-related GTP-binding protein RhoB (RhoB) belongs to the Rho GTP-binding protein family. RhoB facilitates apoptosis in neoplastically transformed cells after DNA damage. RhoB has a negative role in tumorigenesis since deletion causes tumor formation.

Retinoblastoma (RB) is an embryonic malignant neoplasm of retinal origin. It almost always presents in early childhood and is often bilateral. Spontaneous regression ('cure') occurs in some cases. Retinoblastoma acts as a regulator of other genes and forms a complex with adenovirus e1a and with sv40 large t antigen. Retinoblastoma acts as a tumor suppressor and modulats functionally certain cellular proteins with which t and e1a compete for pocket binding. Retinoblastoma is potent inhibitor of e2f-mediated trans-activation, recruits and targets histone methyltransferase suv39h1 leading to epigenetic transcriptional repression, inhibits the intrinsic kinase activity of taf1.

RNA Binding Motif Protein 11 (RBM11) which contains 1 RNA recognition motif is a part of the RBM family. The RBM gene family encodes proteins with an RNA binding motif which participate in the modulation of apoptosis. RBM11 is expressed in testis, kidney, spleen, brain, spinal cord and mammary gland and can be found as 2 isoforms produced by alternative splicing.

Rho-related GTP-binding protein (RhoD) is a member of the small GTPase superfamily. The small GTPase Rho D promotes the rearrangement of the actin cytoskeleton and cell surface and also regulates endosome motility and distribution.

The conserved 76 amino acid protein ubiquitin (Ub) regulates a host of intracellular processes through its enzymatic conjugation to other cellular proteins.
Ubiquitination occurs through sequential steps catalyzed by activating (E1), conjugating (E2), and ligase (E3) enzymes. The final step results in the formation of an isopeptide bond between Ub’s C-terminal glycine residue (G76) and a lysine residue of the target protein, although N-terminal ubiquitination is also known.
Outcomes of this modification include destabilization of the conjugated protein, altered protein trafficking and functional modulation.
After targeting the protein for specific localizations, ubiquitin is released from the substrate by deubiquitinating enzymes.
A mutant ubiquitin, having a Gly to Ala substitution at the C-terminus (G76A ubiquitin) supported several downstream reactions of the proteolytic pathway but inhibits the deubiquitination process.
As consequence, the Ub derivative becomes irreversibly conjugated to protein, shifting the equilibrium between the bound and unbound form in the direction of conjugation, at the expense of the free form.

RHEB is part of the Ras & GTPase superfamily that was originally identified as an immediate-early gene in brain but is also widely expressed in other tissues. RHEB encodes a lipid-anchored, cell membrane protein with five repeats of the RAS-related GTP-binding region. RHEB is necessary in regulation of growth and cell cycle progression due to its role in the TOR/S6K signaling pathway. RHEB has GTPase activity and shuttles between a GDP-bound form and a GTP-bound form, and farnesylation of the protein is required for this activity. RHEB induces oncogenic transformation. RHEB overexpression accelerates lymphomagenesis and is associated with prostate cancer. RHEB can cytopathologically distinguish between fibroadenoma from malignant breast carcinomas which is considered as a secondary diagnostic tool. RHEB has a central role in the regulation of the Ras/B-Raf/C-Raf/MEK signaling network.

TRIM21 is a member of the tripartite motif (TRIM) family. The TRIM motif includes three zinc-binding domains, a RING, a B-box type 1 and a B-box type 2, and a coiled-coil region. The 52 kDa Ro protein is part of the RoSSA ribonucleoprotein, which includes a single polypeptide and one of four small RNA molecules. The RoSSA particle localizes to both the cytoplasm and the nucleus. Ro/SSA interacts with autoantigens in patients with Sjogren syndrome and systemic lupus erythematosus. Ribonucleoprotein particle is composed of a single polypeptide and one of four small RNA molecules. The RoSSA is present in all mammalian cells studied but has no known function. At least 2 isoforms are present in nucleated and red blood cells, and tissue specific differences in Ro/SSA proteins were identified.

Human Retinol Binding Protein, also known as RBP, is responsible for transporting and binding vitamin A. Human RBP has a binding site for 1 molecule of retinol and circulates in the plasma together with prealbumin as a protein complex. The prealbumin binding prevents greater glomerular losses of the human RBP. Only the retinol-free form of the RBP, which has no affinity for prealbumin, undergoes glomerular filtration unhindered as a result of its low Mw. Human RBP is re-absorbed by the tubular cells and catabolized there.

RHOC is a small signaling G protein/GTPase which is part of the Rac subfamily of the family Rho family of GTPases. RHOC rotats between inactive GDP-bound and active GTP-bound states and has a role as a molecular switch in signal transduction cascades. RHOC promotes reorganization of the actin cytoskeleton and regulates cell shape, attachment, and motility.

RANBP1 is a member of a family of proteins which bind Ran GTPase. Ran GTPase is vital for cell cycle control, mRNA processing, nuclear transport, mitotic spindle assembly, and postmitotic nuclear re-assembly and nuclear architecture maintenance. RANBP1 does not stimulate GTPase activity of RAN however RANBP1 does distinctly raise GTP hydrolysis by the RanGTPase-activating protein (RanGAP1). Additionally, RANBP1 operates as a negative regulator of RCC1 by inhibiting RCC1-stimulated guanine nucleotide release from RAN.

R-spondin-3 (RSPO3) belongs to the thrombospondin type 1 repeat supergene family. RSPO3 is a secreted protein which is widely expressed in many tissues. RSPO3 contains 2 Furin-like repeats which have been found in various eukaryotic proteins involved in the mechanism of signal transduction by receptor tyrosine kinases, and one TSP type-1 domain. RSPO3 acts as an activator of the beta-catenin signaling cascade, initiating TCF-dependent gene activation.

E3 ubiquitin ligase RNF4 (RNF4) contains a RING finger motif and functions as a transcription regulator. RNF4 interacts with, and inhibits the activity of, TRPS1, a transcription suppressor of GATA-mediated transcription. Transcription repressor ZNF278/PATZ also interacts with the RNF4 protein thus reducing the enhancement of androgen receptor-dependent transcription mediated by RNF4. RNF4 is broadly expressed at low levels in many tissues and highly expressed in the testis.

RNA Binding Motif Protein 18 (RBM18) is comprised of one RNA recognition motif (RRM) domain.

Retinol binding protein 4(RBP4) belongs to the lipocalin family and is the specific carrier for retinol (vitamin A alcohol) in the blood. This protein was found to be expressed and secreted by adipose tissue, and was strongly associated with insulin resistance. It delivers retinol from the liver stores to the peripheral tissues. In plasma, the RBP-retinol complex interacts with transthyretin which prevents its loss by filtration through the kidney glomeruli.
RBP4 delivers retinol from the liver to the peripheral tissues. In plasma, the rbp-retinol complex interacts with transthyretin, this prevents its loss by filtration through the kidney glomeruli.

E3 ubiquitin-protein ligase RNF181 (RNF181) accepts ubiquitin from an E2 ubiquitin-conjugating enzyme in the thioester form and subsequently directly transfers the ubiquitin to targeted substrates. RNF181 is widely expressed, with the highest levels in the liver and heart and the lowest levels in the brain and skeletal muscle. RNF181 is also expressed in platelets (at protein level).

ADP-ribosylation factor 5 (ARF5) is a small guanine nucleotide-binding protein which enhances the enzymatic activities of cholera toxin. ARF-dependent regulatory mechanisms include the coordination of spectrin interactions with golgi membranes and the connection of actin to the golgi via rho family-dependent G-protein localization and WASP/Arp2/3 complexes. ARF5 is involved in vesicular transport and functioning via phospholipase D activation.

RHOQ (rho-related GTP-binding protein RhoQ) is a small signaling G protein which cycles between an active GTP-bound and an inactive GDP-bound state. In the active state it binds to a diversity of effector proteins to regulate cellular responses. Ras-like protein belongs to the Rac subfamily of the Rho family of GTPases. RHOQ is involved in epithelial cell polarization processes. In addition, RHOQ plays a role in CFTR trafficking to the plasma membrane. RHOQ causes the formation of thin, actin-rich surface projections called filopodia.

ARF1 is a small guanine nucleotide-binding protein that increases the enzymatic activities of cholera toxin. ARF1 is necessary and ubiquitous in eukaryotes. ARF1 takes part in vesicular transport and functioning via phospholipase D activation. ARF1 is involved in membrane traffic and organelle integrity which are closely tied to their reversible association with membranes and distinct interactions with membrane phospholipids.

RELM-beta (Resistin-Like Molecule-beta) is a member of a recently identified family of secreted proteins containing a conserved cystein-rich C-terminus. The RELM family consists of resistin (also called FIZZ3), RELM-alfa (FIZZ1), RELM-beta (FIZZ2) and RELM-gamma. Only resisistin and RELM-beta were found in humans whereas all four RELM family members were identified in rodents.
RELM-beta appears to be produced as a homodimer exclusively by intestinal goblet cells and can be found in high quantities in stool. Remarkably, stool of germ-free mice displaying sterile intestinal tract does not contain RELM-beta until bacterial colonization takes place after pathogen-free mice entered natural environment. Some, but not all, colon carcinoma cell lines secrete RELM-beta into the cell culture supernatant.
The physiological function of RELM-beta is not known. High doses of recombinant RELM-beta showed hyperglycemic effects including lowered glucose disposal and increased hepatic glucose production in mice.

Retinol Binding Protein-2 (RBP2) which is present in the small intestinal epithelium takes part in the uptake and intracellular metabolism of vitamin A. Vitamin A is a fat-soluble vitamin essential for growth, reproduction, differentiation of epithelial tissues, and vision. RBP2 moderates the supply of retinoic acid to the nuclei of endometrial cells throughout the menstrual cycle.

RAB18 belongs to a family of Ras-related small GTPase which is lipid-anchored to the cytoplasmic side of the cell membrane. RAB18 takes part in apical recycling, endocytosis and protein transport between early endosomes and the plasma membrane.

RAB31 Member RAS Oncogene Family (RAB31) is a 194 amino lipid-anchored protein which localizes to the cytoplasmic side of the cell membrane and is a member of the Ras related GTPase superfamily. RAB31 is expressed at high levels in the lung, brain and heart. RAB31 functions in a similar mode to other Rab proteins, namely playing a part in protein transport. Small GTP-binding proteins of the RAB family, for example RAB31, play critical roles in vesicle and granule targeting. RAB31 gas the highest expression in the placenta and brain with lower levels in the heart and lung. However, RAB31 is not detected in liver, skeletal muscle, kidney or pancreas.