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PCNA is located in the nucleus and is a cofactor of DNA polymerase delta. PCNA acts as a homotrimer and helps elevate the processivity of leading strand synthesis during DNA replication. In reaction to DNA damage, PCNA is ubiquitinated and takes part in the RAD6-dependent DNA repair pathway. 2 transcript variants encoding the same protein have been found for PCNA gene. Pseudogenes of this PCNA gene have been described on chromosome 4 and on the X chromosome. PCNA is expressed during late G1- phase, S-phase of mitosis and persists until the end of the M-phase because of its long biological half-life. PCNA is induced by UV irradiation.

Proliferating cell nuclear antigen (PCNA), a protein of 30 kDa molecular weight also known as cyclin, forms a trimer ring around a DNA double-helix. It binds to a variety of other nuclear proteins and thereby organises biochemical processes at the DNA replication fork. PCNA thereby assumes important functions in DNA synthesis, repair and processing, the regulation of cell cycle and even apoptosis.
Anti-PCNA antibodies occur in systemic lupus, where they represent a rare specificity (< 10 % of SLE patients). However, their presence alone or in combination with other autoantibodies should alert the clinician to the presence of defined or evolving SLE.

PCNA is located in the nucleus and is a cofactor of DNA polymerase delta. PCNA acts as a homotrimer and helps elevate the processivity of leading strand synthesis during DNA replication. In reaction to DNA damage, PCNA is ubiquitinated and takes part in the RAD6-dependent DNA repair pathway. 2 transcript variants encoding the same protein have been found for PCNA gene. Pseudogenes of this PCNA gene have been described on chromosome 4 and on the X chromosome. PCNA is expressed during late G1- phase, S-phase of mitosis and persists until the end of the M-phase because of its long biological half-life. PCNA is induced by UV irradiation.

CCNA2 is a member of the highly conserved cyclin family, whose members are characterized by a dramatic periodicity in protein abundance through the cell cycle. Cyclins act as regulators of CDK kinases. Various cyclins demonstrate distinct expression and degradation patterns which contribute to the temporal coordination of each mitotic event. Contrary to cyclin A1, which is present only in germ cells, CCNA2 is expressed in all tissues tested. CCNA2 binds and activates CDC2 or CDK2 kinases, and consequently promotes both cell cycle G1/S and G2/M transitions.

KIAA0101 is a PCNA-binding protein which performs as a regulator of DNA repair all through DNA replication. Subsequent to DNA mutilation, the collaboration with PCNA is interrupted, enabling the interaction between monoubiquitinated PCNA and the translesion DNA synthesis DNA polymerase eta (POLH) at stalled replisomes, assisting the bypass of replication-fork-blocking lesions. Additionally, KIAA0101 performs as a controller of centrosome number.

PEST proteolytic signal containing nuclear protein (PCNP) is a nuclear protein involved in cell cycle regulation and tumorigenesis. The PCNP protein is ubiquitinated post-translationally by NIRF (an ubiquitin ligase). The PCNP exists as 3 isoforms produced by alternative splicing events.

Phosphatidylinositol transfer protein alpha (PITPNA) is found in the cytoplasm, where it catalyzes the transfer of phosphatidylinositol (PI) and phosphatidylcholine (PC) between membranes. PITPNA belongs to a family of lipid-binding proteins which transfer molecules of phosphatidylinositol or phosphatidylcholine between membrane surfaces. PITPNA is implicated in phospholipase C signaling and in the production of phosphatidylinositol 3, 4, 5-trisphosphate (PIP3) by phosphoinositide-3-kinase.

KPNA2 belongs to the karyopherin alpha family. KPNA2 has a vital part in the nuclear import of proteins with a conventional nuclear localization signal (NLS).
In vitro, KPNA2 bound specifically and directly to substrates having a simple or bipartite NLS motif. KPNA2 stimulated docking of import substrates to the nuclear envelope and together with Ran reconstituted complete nuclear protein import.

Cyclin-dependent kinase inhibitors (CDKIs) are proteins that bind to and inhibit the activity of CDKs. Two major classes of CDK inhibitors have been identified. The p16 family (p15, p16, p18 and p19) binds to and inhibits the activities of CDK4 and CDK6. The p21 family (p21, p27, p28 and p57) can bind to broad range of CDK-cyclin complexes and inhibit their activities. CDKIs are capable of suppressing growth, and several lines of evidence strongly suggest that at least some CDKIs may be tumor suppressor proteins.

The Regulatory (R) subunit of Protein Kinase A (PKA) inhibits its kinase activity by shielding the Catalytic (C) subunit from physiological substrates. This inhibition is reversed in response to extra-cellular signals that increase cAMP levels in the cytoplasm. Upon cAMP binding to R, C is allosterically released from R, activating a spectrum of downstream signaling cascades. Crystallographic data indicated that a series of distinct conformational changes within CBD-A must occur to relay the cAMP signal from the cAMP binding site to the R:C interaction interface. One critical cAMP relay site within the CBD-A of R has been identified as Asp170 because the D170A mutation selectively reduces the negative cooperativity between the cAMP- and C-recognition sites (i.e. the KD for the R:C complex in the presence of cAMP is reduced by more than 12-fold), without significantly compromising the high affinity of R for both binding partners.

The protein kinase A holoenzyme is a heterotetramer composed of two types of subunits: Catalytic and Regulatory. The Catalyticsubunit contains the enzyme's active site. It also contains a domain that binds ATP and a domain that binds the regulatory subunit. The Regulatory subunit consists oftwo molecules which bind one another in an anti-parallel orientation to form a homodimer; for type I subunits- this binding is covalent via disulfide bonds. This subunit also has has two domains that bind cyclic AMP, a domain that interacts with a catalytic subunit, and an "auto-inhibitory" domain that serves as a substrate or pseudosubstrate for the catalytic subunit. Regulatory subunits may also have biologic activity distinct from their role in modulating catalytic subunit activity. Regulatory subunits exist in two major forms, RI and RII, with each form having two subtypes designated alpha and beta. Each of the four isotypes of the regulatory subunit is encoded by a different gene. In addition, three isotypes of the catalytic subunit have been identified (alpha, beta and gamma). The different isotypes tend to have different distributions within cells and among tissues. Type I enzymes inhabit cytoplasmic, soluble fractions of the cell, whereas type II enzymes tend to associate with cellular membranes.

Polymerase (DNA Directed), Epsilon 3, also know as POLE3, is a histone-fold protein which interacts with other histone-fold proteins to bind DNA in a sequence-independent manner. These histone-fold protein dimers merge into larger enzymatic complexes for DNA transcription, replication, and packaging.

Heterogeneous nuclear ribonucleoprotein A1 (HNRNPA1) is a member of the A/B subfamily of ubiquitously expressed heterogeneous nuclear ribonucleoproteins (hnRNPs). HNRNPA1 is involved in the packing of pre-mRNA into hnRNP particles, transport of poly(A) mRNA from the nucleus to the cytoplasm and may control splice site selection. The HNRNPA1 protein may also have a role in HCV RNA replication. In addition, HNRNPA1 is believed to have a key role in the formation of specific myometrial protein species in parturition.
The hnRNP proteins have distinctive nucleic acid binding properties. HNRNPA1 has 2 repeats of quasi-RRM domains that bind to RNAs. HNRNPA1 is one of the most copious core proteins of hnRNP complexes and it is restricted to the nucleoplasm. The HNRNPA1 protein, along with other hnRNP proteins, is exported from the nucleus, most likely bound to mRNA, and is immediately re-imported. The M9 domain of HNRNPA1 functions as both a nuclear localization and nuclear export signal.

P85a functions as the regulatory subunit of the class IA PI3-kinase isoforms a, b, and d.
It contains two SH2 domains that bind to tyrosine-phosphorylated growth factor receptors or substrate adaptor proteins.
It also contains a BH (breakpoint cluster region homology) domain that shows GAP activity towards the small GTPases Rab4, Rab5, Cdc42, Rac1 and to a lesser extend towards Rab6 and Rab11.
It was shown that PI3Ka catalytic subunit mediated phosphorylation of the p85a adapter reduces the lipid kinase activity of the heterodimer and this gives hints for PI3K-dependent signaling events not requiring production of 3’-phosphorylated phosphoinositides.
PI3Ka protein kinase activity has been implicated in IRS-1 serine phosphorylation in insulin-treated adipocytes and in STAT3 and IRS-1 phosphorylation upon activation of the type 1 IFN receptor by IFN-a.

Persephin is a member of the GDNF ligand subfamily of the TGF-beta superfamily. PSPN encourages the existence and growth of key dopaminergic and motor neurons, as well as taking part in kidney development. Nonetheless, persephin does not support existence of peripheral neurons.

a-Synuclein (amino acids 1-140), an acidic neuronal protein of 140 amino acids, is extremely heat-resistant and is natively unfolded with an extended structure primarily composed of random coils. a-synuclein has been suggested to be implicated in the pathogenesis of Parkinson’s disease and related neurodegenerative disorders, and more recently, to be an important regulatory component of vesicular transport in neuronal cells. Moreover, recent studies have shown that a-synuclein has chaperone activity and that this activity is lost upon removing its C-terminal acidic tail (amino acids 96-140).

Cyclin-dependent kinase inhibitors (CDKIs) are proteins that bind to and inhibit the activity of CDKs. Two major classes of CDK inhibitors have been identified. The p16 family (p15, p16, p18 and p19) binds to and inhibits the activities of CDK4 and CDK6. The p21 family (p21, p27, p28 and p57) can bind to broad range of CDK-cyclin complexes and inhibit their activities. CDKIs are capable of suppressing growth, and several lines of evidence strongly suggest that at least some CDKIs may be tumor suppressor proteins.

HNRNPC is a member of the subfamily of ubiquitously expressed heterogeneous nuclear ribonucleoproteins (hnRNPs) which are related to pre mRNAs in the nucleus and effect pre mRNA processing and other aspects of mRNA metabolism and transport. Although all of the hnRNPs are present in the nucleus, several hnRNPs travel between the nucleus and the cytoplasm. The hnRNP proteins have specific nucleic acid binding properties.

The protein kinase A holoenzyme is a heterotetramer composed of two types of subunits: Catalytic and Regulatory. The Catalyticsubunit contains the enzyme's active site. It also contains a domain that binds ATP and a domain that binds the regulatory subunit. The Regulatory subunit consists oftwo molecules which bind one another in an anti-parallel orientation to form a homodimer; for type I subunits- this binding is covalent via disulfide bonds. This subunit also has has two domains that bind cyclic AMP, a domain that interacts with a catalytic subunit, and an "auto-inhibitory" domain that serves as a substrate or pseudosubstrate for the catalytic subunit. Regulatory subunits may also have biologic activity distinct from their role in modulating catalytic subunit activity. Regulatory subunits exist in two major forms, RI and RII, with each form having two subtypes designated alpha and beta. Each of the four isotypes of the regulatory subunit is encoded by a different gene. In addition, three isotypes of the catalytic subunit have been identified (alpha, beta and gamma). The different isotypes tend to have different distributions within cells and among tissues. Type I enzymes inhabit cytoplasmic, soluble fractions of the cell, whereas type II enzymes tend to associate with cellular membranes.

TIE-1 (tyrosine kinase with Ig and EGF homology domains 1) and TIE-2/Tek comprise a receptor tyrosine kinase (RTK) subfamily with unique structural characteristics: two immunoglobulin-like domains flanking three epidermal growth factor (EGF)-like domains and followed by three fibronectin type III-like repeats in the extracellular region and a split tyrosine kinase domain in the cytoplasmic region. These receptors are expressed primarily on endothelial and hematopoietic progenitor cells and play critical roles in angiogenesis, vasculogenesis and hematopoiesis. Human TIE-1 cDNA encodes a 1124 amino acid (aa) residue precursor protein with an 18 residue putative signal peptide, a 727 residue extracellular domain and a 354 residue cytoplasmic domain. Whereas two ligands have been described for TIE-2 [angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2)], so far no ligand was found for TIE-1.

DnaJ, Heat shock protein, functions in association with DnaK(Hsp70) molecular chaperone to facilitate protein folding. p70 chaperone. DnaJ plays a key role in the chaperone reaction by stimulating the ATPase activity and activating the substrate binding of Hsp70. DnaJ consists of four domains that are N-terminal 76 amino acid J-domain, G/F domain, zinc-binding cystein rich CR-domain, C-terminal CTD-domain and they are conserved to various degrees among the homologues.

Ku antigen consists of two polypeptides (70 kDa and 80 kDa; the p80 subunit is occasionally called p86). The Ku heterodimer provides DNA-binding and regulatory functions to DNA-dependent protein kinase which is a central enzyme for DNA recombination processes in eucaryotic cells. The Ku protein plays important roles in multiple nuclear processes including DNA repair, V(D)J recombination, telomere maintenance, and the regulation of specific gene transcription.
Antibodies to Ku were originally reported in scleroderma-polymyositis overlap syndrome (up to 20% of patients) but have also been detectable in about 20 % of patients with primary pulmonary hypertension (as a complication of overlap), in 5-10 % of SLE and MCTD patients, and in up to 20 % of patients with primary Sj?gren's syndrome.
In IIF using HEp-2 cells, Ku-positive sera yield a dense, fine granular pattern with nucleolar staining that is typical but not specific for anti-Ku. Detection of Ku antibodies by Western blot may bear false-negative results since the main reactive epitope on the p70/p80 heterodimer is conformation-dependent.

PNP is a member of the PNP/MTAP phosphorylase family of proteins. PNP catalyzes the reversible phosphorolysis of ribonucleosides and 2’-deoxyribonucleosides with specificity for guanine, hypoxanthine and their analogs. PNP deficiency is a rare autosomal recessive genetic disease linked to a severe defect in T-lymphocyte function and neurologic disorder in children, comprising four percent of combined immunodeficiency cases.