Characterization of the Replication Initiator Orc1/Cdc6 from the Archaeon Picrophilus torridus

Eukaryotic DNA replication is preceded by the assembly of prereplication complexes (pre-RCs) at or very near origins in G₁ phase, which licenses origin firing in S phase. The archaeal DNA replication machinery broadly resembles the eukaryal apparatus, though simpler in form. The eukaryotic replication initiator origin recognition complex (ORC), which serially recruits Cdc6 and other pre-RC proteins, comprises six components, Orc1-6. In archaea, a single gene encodes a protein similar to both the eukaryotic Cdc6 and the Orc1 subunit of the eukaryotic ORC, with most archaea possessing one to three Orc1/Cdc6 orthologs. Genome sequence analysis of the extreme acidophile Picrophilus torridus revealed a single Orc1/Cdc6 (PtOrc1/Cdc6). Biochemical analyses show MBP-tagged PtOrc1/Cdc6 to preferentially bind ORB (origin recognition box) sequences. The protein hydrolyzes ATP in a DNA-independent manner, though DNA inhibits MBP-PtOrc1/Cdc6-mediated ATP hydrolysis. PtOrc1/Cdc6 exists in stable complex with PCNA in Picrophilus extracts, and MBP-PtOrc1/Cdc6 interacts directly with PCNA through a PIP box near its C terminus. Furthermore, PCNA stimulates MBP-PtOrc1/Cdc6-mediated ATP hydrolysis in a DNA-dependent manner. This is the first study reporting a direct interaction between Orc1/Cdc6 and PCNA in archaea. The bacterial initiator DnaA is converted from an active to an inactive form by ATP hydrolysis, a process greatly facilitated by the bacterial ortholog of PCNA, the β subunit of Pol III. The stimulation of PtOrc1/Cdc6-mediated ATP hydrolysis by PCNA and the conservation of PCNA-interacting protein motifs in several archaeal PCNAs suggest the possibility of a similar mechanism of regulation existing in archaea. This mechanism may involve other yet to be identified archaeal proteins.     

Mapping of genetic modifiers affecting the eye phenotype of ocular retardation (Chx10 or-J ) mice

Ocular retardation is a recessive murine mutation whose phenotypic expression is greatly affected by genetic background effects. Mice of the inbred 129/SvJ background that are homozygous for the Chx10^or-J mutation are blind and have a thin, poorly differentiated retina and no optic nerve. A backcross between 129/SvJ and Mus musculus castaneus (CASA/Rk) produced animals that were homozygous for the Chx10^or-J mutation, yet showed a much milder phenotype. Such animals, when brother-sister mated and selected for mild phenotype for several generations, resulted in partial recovery of visual function, including presence of an optic nerve and pupillary response. In this article we report a genome scan of phenotypic extremes of the backcross to identify the genetic loci affecting this phenotype modification. Our scan revealed significant loci on Chromosomes 6 and 14 where the CASA/Rk alleles are maintained selectively. Markers were developed near candidate genes, but no candidate gene could be identified unequivocally. Electronic Supplementary Material Electronic Supplementary material is available for this article at and accessible for authorised users.     

Isolation and characterization of a fatty acyl esterase from rat lung

In an effort to facilitate studies of the reaction involved in the removal of fatty acids from acyl proteins, we have synthesized an octanoic acid ester of doubly blocked serine, specifically octanoyl N-carbobenzoxy-L-serine-benzyl ester (octanoyl boc-serine), and used it as a substrate to guide the purification of an esterase from rat lung. The esterase was purified 228-fold by column chromatography on DE-52 cellulose, hydroxylapatite, octyl-Sepharose, and concanavalin A-Sepharose and by HPLC gel filtration. The final enzyme preparation ran as a single 77,000-Da band when subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and exhibited a single symmetrical peak (sedimentation coefficient, 4.5 S) when centrifuged through a sucrose density gradient (empirical Mr, 63,000). The esterase is an acidic protein, pI 4.1, and is very active against p-nitrophenyl esters comprised of C4-C14 fatty acids; the highest specific activity (26.5 mumol/min/mg) was obtained using p-nitrophenyl caprylate as substrate. The pH optimum of the lung esterase is near 8.0 and the activity on octanoyl boc-serine is maximum when 0.3% (w/v) Myrj-52 is included in the assay medium. The activity of the esterase is not dependent on calcium ions. The enzyme does not remove acyl groups from the G-protein of vesicular stomatitis virus or the proteolipid of bovine brain. The possible role of the esterase in the metabolism of acylated proteins is considered.     

Disubstituted Dithiolethione ACDT Exerts Neuroprotective Effects Against 6-Hydroxydopamine-Induced Oxidative Stress in SH-SY5Y Cells

Neurochemical Research - Parkinson’s disease (PD) is a prevalent, progressive, neurodegenerative disorder with no known cure. Oxidative stress has been found to play a significant role in its...     

Alpha-galactoside-binding isolectins from wild jack fruit seed (Artocarpus hirsuta): purification and properties

Five isolectins with marked specificity for alpha-linked galactose were purified from the wild jack (Artocarpus hirsuta) seeds by affinity chromatography on cross-linked guar gum. They were composed of a glycosylated subunit A (Mr = 16 kDa) and a nonglycosylated subunit B (Mr = 11 kDa) in noncovalent association. The isolectins which eluted as a single peak of Mr 45 kDa on gel filtration in Biogel P-100 and in a TSK G-3000 SW high pressure column, were resolved into five peaks on electrophoresis at pH 4.5. Sodium dodecyl sulphate polyacrylamide gel electrophoreogram of the major isolectin band suggested that the isolectins may be the five possible tetrameric combinations of A and B subunits. The combined isolectins bound only two molecules of 4-methyl umbelliferyl alpha-D-galactoside with a binding constant of 4.75 x 10(4) M-1. The pH optimum of sugar binding was 7.0. The isolectins specifically bound to human IgG and IgA but not to IgM.