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Transforming growth factor β (TGF-β)-mediated G1 arrest previously has been shown to specifically target inactivation of cyclin D:cyclin-dependent kinase (Cdk) 4/6 complexes. We report here that TGF-β-treated human HepG2 hepatocellular carcinoma cells arrest in G1, but retain continued cyclin D:Cdk4/6 activity and active, hypophosphorylated retinoblastoma tumor suppressor protein. Consistent with

Cyclin-dependent kinase (CDK)-activating kinases (CAKs) carry out essential activating phosphorylations of CDKs such as Cdc2 and Cdk2. The catalytic subunit of mammalian CAK, MO15/Cdk7, also functions as a subunit of the general transcription factor TFIIH. However, these functions are split in budding yeast, where Kin28p functions as the kinase subunit of TFIIH and Cak1p functions as a CAK. We sho

Cell cycle progression is regulated by cyclin-dependent kinases (cdks). The activity of cdks is tightly controlled by several mechanisms, including binding of subunits to cdks (cyclins and inhibitors), and phosphorylation events. This review focuses on the activating phosphorylation of cdks by an enzyme termed cdk-activating kinase (CAK). Two classes of CAKs have been identified: monomeric Cak1p f

Activating phosphorylation of cyclin-dependent protein kinases (CDKs) is necessary for their kinase activity and cell cycle progression. This phosphorylation is carried out by the Cdk-activating kinase (CAK); in contrast, little is known about the corresponding protein phosphatase. We show that type 2C protein phosphatases (PP2Cs) are responsible for this dephosphorylation of Cdc28p, the major bud

Eukaryotic cell cycles are controlled by the activities of cyclin-dependent kinases (cdks). The major cdk in budding yeast, Saccharomyces cerevisiae, is Cdc28p. Activation of Cdc28p requires phosphorylation on threonine 169 and binding to a cyclin. Thr-169 is phosphorylated by the cdk-activating kinase (CAK), Cak1p, which was recently identified as the physiological CAK in budding yeast. Here we p

Cell cycle progression is controlled by the sequential functions of cyclin-dependent kinases (cdks). Cdk activation requires phosphorylation of a key residue (on sites equivalent to Thr-160 in human cdk2) carried out by the cdk-activating kinase (CAK). Human CAK has been identified as a p40(MO15)/cyclin H/MAT1 complex that also functions as part of transcription factor IIH (TFIIH) where it phospho

Spermatozoa have a defined function, that is, the fertilization of an egg. To achieve this goal, spermatozoa have to move actively toward the egg and inject the male pronucleus into the egg. Therefore, sperm motility is one of the crucial determinants for male fertility. Surprisingly, however, structure and energy metabolism can differ substantially between spermatozoa from different species. Here

Activation of the cyclin-dependent kinases to promote cell cycle progression requires their association with cyclins as well as phosphorylation of a threonine (residue 161 in human p34(cdc2)). This phosphorylation is carried out by CAK, the Cdk-activating kinase. We have purified and cloned CAK from S. cerevisiae. Unlike CAKs from other organisms, Cak1p is active as a monomer, has full activity wh

Creatine kinase (CK) isoenzymes, with emphasis on the mitochondrial CK isoenzymes, were characterized and localized in chicken cerebellum. Chicken cerebellar extracts analyzed by two-dimensional gels, using anti-peptide antibodies specific for sarcomeric muscle-type mitochondrial CK (Mib-CK) and revealed the presence of a Mib-CK variant in avian cerebellum. This CK isoform was localized by immunof

The creatine kinase (CK) isoenzyme system is essential for motility in rooster and sea urchin sperm. In the present study, biochemical characterization as well as immunofluorescence and confocal laser microscopy with highly specific antibodies against various chicken CK isoenzymes revealed that cytosolic brain-type CK isoenzyme (B-CK) is the only CK isoenzyme in rooster seminal plasma, while three

Mitochondrial creatine kinase (Mi-CK) consists of octameric and dimeric molecules that are interconvertible. In the present study, the kinetic properties of purified chicken heart Mi-CK (Mi(b)-CK) dimers and octamers were investigated separately under highly controlled conditions. Gel-permeation chromatography was performed before and after kinetic measurements in order to clearly define the propo

An interaction of mitochondrial creatine kinase with purified outer mitochondrial porin (voltage-dependent anion channel) was shown by co- sedimentation assays as well as by gel permeation chromatography. Porin formed high M(r) complexes with wild-type mitochondrial creatine kinase as well as with an N-terminal deletion mutant, lacking the first five N-terminal amino acids. The complexes were iden

Mitochondrial creatine kinase (Mi-CK) isoenzymes, in contrast to cytosolic CKs, form octameric molecules composed of four stable dimers. Octamers and dimers are interconvertible. Removal of the N-terminal pentapeptide of chicken cardiac Mi-CK (Mib-CK) by limited proteolysis drastically destabilized the octamer. The role of the charged amino acids within the N-terminal heptapeptide was studied in d

Sarcomeric mitochondrial creatine kinase (Mi(b)-CK) of chicken was expressed in Escherichia coli as a soluble enzyme by using an inducible phage-T7 promoter. Up to one third of the protein in E. coli extracts consisted of soluble recombinant Mi(b)-CK in an enzymically active form. Approx. 20 mg of nearly-homogenous Mi(b)-CK was isolated in a two-step isolation procedure starting with 1 litre of is

Since 2010 when the North American ELKHORN and Baltoscandic PAROVEJA isotope excursions were first described and named, their mutual age relations have remained uncertain, if not controversial. This was at least partly due to the incompleteness of the ELKHORN excursion in its reference section in western Ohio. The unexpected discovery of an apparently complete ELKHORN excursion in a drill core fro