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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Saccharomyces cerevisiae SRK1 gene, when expressed on a low-copy shuttle vector, partially suppresses the phenotype associated with elevated levels of cyclic AMP-dependent protein kinase activity and suppresses the temperature-sensitive cell cycle arrest of the ins1 mutant. SRK1 is located on chromosome IV, 3 centimorgans from gcn2. A mutant carrying a deletion mutation in srk1 is viable. SRK1 encodes a 140-kDa protein with homology to the dis3+ protein from Schizosaccharomyces pombe. The ability of SRK1 to alleviate partially the defects caused by high levels of cyclic AMP-dependent protein kinase and the similarity of its encoded protein to dis3+ suggest that SRK1 may have a role in protein phosphatase function.
Mol Cell Biol 1991 Jun
PMID:The Saccharomyces cerevisiae SRK1 gene, a suppressor of bcy1 and ins1, may be involved in protein phosphatase function. 164 49

Saccharomyces cerevisiae genomic clones that encode calmodulin-binding proteins were isolated by screening a lambda gt11 expression library using 125I-labeled calmodulin as probe. Among the cloned yeast genes, we found two closely related genes (CMP1 and CMP2) that encode proteins homologous to the catalytic subunit of phosphoprotein phosphatase. The presumed CMP1 protein (62,999 Da) and CMP2 protein (68,496 Da) contain a 23 amino acid sequence very similar to those identified as calmodulin-binding sites in many calmodulin-regulated proteins. The yeast genes encode proteins especially homologous to the catalytic subunit of mammalian phosphoprotein phosphatase type 2B (calcineurin). The products of the CMP1 and CMP2 genes were identified by immunoblot analysis of cell extracts as proteins of 62,000 and 64,000 Da, respectively. Gene disruption experiments demonstrated that elimination of either or both of these genes had no effect on cell viability, indicating that these genes are not essential for normal cell growth.
Mol Gen Genet 1991 May
PMID:The Saccharomyces cerevisiae genes (CMP1 and CMP2) encoding calmodulin-binding proteins homologous to the catalytic subunit of mammalian protein phosphatase 2B. 164 87

Protein phosphatase 2A1 was purified from rat skeletal muscle and used to produce antisera to the three subunits of the holoenzyme. Affinity purified antibodies specific for the subunits of the phosphatase enzyme were found to recognize the type 2A1 and 2A2 phosphatase from rat skeletal muscle, heart, liver, brain and erythrocytes and were used to investigate the effects of diabetes on the levels of this enzyme in liver and heart. Phosphorylase phosphatase assays coupled with immunoblot analysis of fractionated rat liver and heart cytosol from normal and diabetic animals show no apparent differences in the quantity or activity of these enzymes following the induction of alloxan diabetes. When considering these results and the normal physiological concentrations of known effectors of these enzymes, it is likely that protein phosphatase 2A1 and 2A2 are not responsible for the dephosphorylation of phosphorylase a under physiological conditions.
Mol Cell Biochem 1991 Mar 13
PMID:Purification and the immunological characterization of rat protein phosphatase 2A: enzyme levels in diabetic liver and heart. 165 Apr 27

We have cloned three genes for protein phosphatases in the yeast Saccharomyces cerevisiae. Two of the genes, PPH21 and PPH22, encode highly similar proteins that are homologs of the mammalian protein phosphatase 2A (PP2A), while the third gene, PPH3, encodes a new PP2A-related protein. Disruptions of either PPH21 or PPH22 had no effects, but spores disrupted for both genes produced very small colonies with few surviving cells. We conclude that PP2A performs an important function in yeast cells. A disruption of the third gene, PPH3, did not in itself affect growth, but it completely prevented growth of spores disrupted for both PPH21 and PPH22. Thus, PPH3 provides some PP2A-complementing activity which allows for a limited growth of PP2A-deficient cells. Strains were constructed in which we could study the phenotypes caused by either excess PP2A or total PP2A depletion. We found that the level of PP2A activity has dramatic effects on cell shape. PP2A-depleted cells develop an abnormal pear-shaped morphology which is particularly pronounced in the growing bud. In contrast, overexpression of PP2A produces more elongated cells, and high-level overexpression causes a balloonlike phenotype with huge swollen cells filled by large vacuoles.
Mol Cell Biol 1991 Oct
PMID:Protein phosphatase 2A in Saccharomyces cerevisiae: effects on cell growth and bud morphogenesis. 165 15

Microscopic screening of a collection of cold-sensitive mutants of Saccharomyces cerevisiae led to the identification of a new gene, CDC55, which appears to be involved in the morphogenetic events of the cell cycle. CDC55 maps between CDC43 and CHC1 on the left arm of chromosome VII. At restrictive temperature, the original cdc55 mutant produces abnormally elongated buds and displays a delay or partial block of septation and/or cell separation. A cdc55 deletion mutant displays a cold-sensitive phenotype like that of the original isolate. Sequencing of CDC55 revealed that it encodes a protein of about 60 kDa, as confirmed by Western immunoblots using Cdc55p-specific antibodies. This protein has greater than 50% sequence identity to the B subunits of rabbit skeletal muscle type 2A protein phosphatase; the latter sequences were obtained by analysis of peptides derived from the purified protein, a polymerase chain reaction product, and cDNA clones. An extragenic suppressor of the cdc55 mutation lies in BEM2, a gene previously identified on the basis of an apparent role in bud emergence.
Mol Cell Biol 1991 Nov
PMID:CDC55, a Saccharomyces cerevisiae gene involved in cellular morphogenesis: identification, characterization, and homology to the B subunit of mammalian type 2A protein phosphatase. 165 38

We have used okadaic acid (OA), a cell-permeable inhibitor of serine/threonine protein phosphatase types 1 (PP-1) and 2A (PP-2A), to demonstrate that the subcellular distribution of glucocorticoid receptor (GR) in rat fibroblasts is influenced by its phosphorylation state. Nuclear GRs in OA-treated cells retain transcriptional enhancement activity. Nuclear import or export of hormone agonist-bound GRs is not affected by OA. However, a dose of OA that fully inhibits PP-2A and partially inhibits PP-1, but not a lower dose that only partially inhibits PP-2A, leads to inefficient nuclear retention of agonist-bound GRs, and their redistribution into the cytoplasm. These receptors appear to be trapped in the cytoplasmic compartment and are unable to recycle (i.e. reenter the nucleus). Addition of OA during different steps of GR recycling demonstrates that OA must be present during nuclear export of GRs to block GR recycling. A direct role for PP-1 and/or PP-2A in GR recycling is suggested by site-specific hyperphosphorylation of GRs in vivo during OA inhibition of recycling. These are the same sites that undergo in vitro site-specific dephosphorylation by PP-1 and PP-2A. The block in GR recycling that results from inhibition of PP-1 and/or PP-2A resembles effects previously observed in v-mos-transformed rat fibroblasts. Interestingly, OA inhibition of PP-2A in v-mos-transformed cells leads to the reversal of oncoprotein effects on GR recycling and retention of receptors within the nuclear compartment. We propose that GR recycling is influenced by the activities of distinct protein phosphatases (PP-1 and/or PP-2A), and that the interference of this pathway observed in v-mos-transformed cells may be the result of effects of the oncoprotein on the phosphatases or a specific subset of their targets.
Mol Endocrinol 1991 Sep
PMID:Protein phosphatase types 1 and/or 2A regulate nucleocytoplasmic shuttling of glucocorticoid receptors. 166 12

Oligonucleotides corresponding to highly conserved regions of mammalian protein phosphatase catalytic subunits were used in the polymerase chain reaction (PCR) to generate an amplification product from genomic DNA of Trypanosoma brucei rhodesiense. The PCR product was used to screen a T. b. rhodesiense cDNA library for cDNA clones encoding putative protein phosphatase catalytic subunits. Two cDNA clones, (TPP1A and TPP1B) representing two distinct type 1 catalytic subunit isotypes, encode 39-kDa proteins of 346 amino acids that show 66% and 40% identity, respectively, to mammalian protein phosphatase 1 and 2A catalytic subunits. Both cDNAs are derived from 2.3-kb mRNAs, and Northern blot analysis has provided indirect evidence that these mRNAs are part of the same transcription unit as mRNAs for RNA polymerase II largest subunit. Another cDNA, TPP2, represents the type 2A class of phosphatases and codes for a 34.5-kDa protein of 303 amino acids. The deduced amino acid sequence has 39% and 55% identity, respectively, to the catalytic subunits of mammalian protein phosphatase 1 and 2A. Southern and Northern blot analyses are consistent with TPP2 being encoded by a single copy gene from which is derived a mRNA of 2.5 kb. This finding constitutes the first example in eukaryotes in which a single gene encodes the type 2A class of protein phosphatases. Sera from mice immunized with TPP1A fusion protein reacted with the catalytic subunits of mammalian types 1, 2A and 2B protein phosphatases. However, antisera to TPP2 fusion protein was specific for the type 2A catalytic subunit and recognized a polypeptide of 35 kDa in a Western blot of crude trypanosomal lysate.
Mol Biochem Parasitol 1991 Dec
PMID:Characterization of trypanosome protein phosphatase 1 and 2A catalytic subunits. 166 79

Data emerging from a number of different systems indicate that protein phosphatases are highly regulated and potentially responsive to changes in the levels of intracellular second messengers produced by extracellular stimulation. They may therefore be involved in the regulation of many cell functions. The protein phosphatases in the nervous system have not been well studied. However, a number of neuronal-specific regulators (such as DARPP-32 and G-substrate) exist, and brain protein phosphatases appear to have particularly low specific activity, suggesting that neuronal protein phosphatases possess considerable and unique potential for regulation. Several early events following depolarization or receptor activation appear to involve specific dephosphorylations, indicating that regulation of protein phosphatase activity is important for the control of many neuronal functions. This article reviews the current literature concerning the identification, regulation, and function of serine/threonine protein phosphatases in the brain, with particular emphasis on the regulation of the major protein phosphatases, PP1 and PP2A, and their potential roles in modulating neurotransmitter release and postsynaptic responses.
Mol Neurobiol 1991
PMID:The regulation and function of protein phosphatases in the brain. 166 87

The interferon-induced double-stranded RNA-dependent eIF-2 alpha kinase (dsI) has an established role in mediating part of interferon's antiviral effects. Numerous studies have suggested that dsI also has regulatory functions in cells not infected with virus. Our previous results have indicated that the activation of this kinase may be an important regulatory signal in controlling growth arrest of mouse 3T3-F442A fibroblasts prior to their subsequent differentiation to adipocytes. Here, we report that extracts from 3T3-F442A cells cultured under conditions nonpermissive for differentiation exhibit significantly reduced dsI activity and that this reduction is due, at least in part, to the presence of elevated levels of a novel inhibitor of dsI activation (dRF). This inhibitor is also detected in reduced amounts in extracts from cells cultured under conditions which are permissive for differentiation. We have achieved a 1,000-fold purification of dRF activity, and highly purified dRF preparations were found to be greatly enriched for a 15-kDa protein that was greater than 90% pure. Our results indicate that dRF is not a protein phosphatase or protease but a reversible inhibitor of dsI autophosphorylation. In addition, our results imply that dRF is a physiologic regulator of dsI, since dRF activity correlates with the ability of 3T3-F442A cells to undergo adipose conversion.
Mol Cell Biol 1991 Jun
PMID:Partial characterization of a cellular factor that regulates the double-stranded RNA-dependent eIF-2 alpha kinase in 3T3-F442A fibroblasts. 167 19

This article focuses on the role of protein phosphorylation, especially that mediated by protein kinase C (PKC), in neurotransmitter release. In the first part of the article, the evidence linking PKC activation to neurotransmitter release is evaluated. Neurotransmitter release can be elicited in at least two manners that may involve distinct mechanisms: Evoked release is stimulated by calcium influx following chemical or electrical depolarization, whereas enhanced release is stimulated by direct application of phorbol ester or fatty acid activators of PKC. A markedly distinct sensitivity of the two pathways to PKC inhibitors or to PKC downregulation suggests that only enhanced release is directly PKC-mediated. In the second part of the article, a framework is provided for understanding the complex and apparently contrasting effects of PKC inhibitors. A model is proposed whereby the site of interaction of a PKC inhibitor with the enzyme dictates the apparent potency of the inhibitor, since the multiple activators also interact with these distinct sites on the enzyme. Appropriate PKC inhibitors can now be selected on the basis of both the PKC activator used and the site of inhibitor interaction with PKC. In the third part of the article, the known nerve terminal substrates of PKC are examined. Only four have been identified, tyrosine hydroxylase, MARCKS, B-50, and dephosphin, and the latter two may be associated with neurotransmitter release. Phosphorylation of the first three of these proteins by PKC accompanies release. B-50 may be associated with evoked release since antibodies delivered into permeabilized synaptosomes block evoked, but not enhanced release. Dephosphin and its PKC phosphorylation may also be associated with evoked release, but in a unique manner. Dephosphin is a phosphoprotein concentrated in nerve terminals, which, upon stimulation of release, is rapidly dephosphorylated by a calcium-stimulated phosphatase (possibly calcineurin [CN]). Upon termination of the rise in intracellular calcium, dephosphin is phosphorylated by PKC. A priming model of neurotransmitter release is proposed where PKC-mediated phosphorylation of such a protein is an obligatory step that primes the release apparatus, in preparation for a calcium influx signal. Protein dephosphorylation may therefore be as important as protein phosphorylation in neurotransmitter release.
Mol Neurobiol 1991
PMID:The role of protein kinase C and its neuronal substrates dephosphin, B-50, and MARCKS in neurotransmitter release. 168 57


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