The phosphoprotein phosphatase 1 (PP1) catalytic subunit encoded by the Saccharomyces GLC7 gene is involved in control of glycogen metabolism, meiosis, translation, chromosome segregation, cell polarity, and G 2 /M cell cycle progression. It is also lethal when overproduced. We have isolated strains which are resistant to Glc7p overproduction lethality as a result of mutations in the SHP1 (suppressor of high-copy PP1) gene, which was previously encountered in a genomic sequencing project as an open reading frame whose interruption totally blocked sporulation and slightly slowed cell proliferation. These phenotypes also characterized our shp1 mutations, as did deficient glycogen accumulation. Lysates from the shp1 mutants were deficient in PP1 catalytic activity but exhibited no obvious abnormalities in the steady-state level or subcellular localization pattern of a catalytically active Glc7p-hemagglutinin fusion polypeptide. The lower level of PP1 activity in shp1 cells permitted substitution of a galactose-induced GAL10-GLC7 fusion for GLC7; depletion of Glc7p from these cells by growth in glucose medium resulted in G 2 /M arrest as previously observed for a glc7 cs allele but with depletion arrest occurring most frequently at a later stage of mitosis. The higher requirement of glycogen accumulation and sporulation for PP1 activity would permit their regulation via Glc7p activity, independent of its requirement for mitosis.During the last several years, studies employing fungal genetics have begun to make a major contribution to our understanding of the roles that serine/threonine phosphoprotein phosphatases (PPs) play in the control of vital processes in eukaryotic cells. The need for genetic analysis seems particularly acute for PP1 and PP2A, whose broad substrate and pathway specificities could hamper the resolution of regulatory questions by purely biochemical approaches (14, 44). The homolog of the mammalian PP1 catalytic subunit that is encoded by the GLC7 gene of Saccharomyces cerevisiae is essential for viability (17). At its restrictive temperature, a glc7 cs mutant ceases growth at G 2 /M (23), which is reminiscent of the Mphase growth arrest exhibited by PP1 conditional mutants of Aspergillus nidulans (15) and Schizosaccharomyces pombe (31,32). Other, nonlethal mutations in GLC7 implicate it in control of mitotic chromosome segregation (18), of glycogen metabolism (33), of meiosis and/or sporulation (11), of bud emergence (23), and of control of translation via dephosphorylation of eukaryotic initiation factor 2␣ (eIF-2␣) (55). Wild-type GLC7 is also lethal when overexpressed by fusion to a strong promoter (26) or by cloning on an inducible high-copy vector (see below). Lower levels of overexpression lead to decreased fidelity of chromosome segregation (18).In its effect on these disparate processes, it is still unclear whether Glc7p is actively regulatory, i.e., variably affecting the target process in response to an upstream effector or signal, or whether it is merely acting as a counterpoise to on...

The geometries, vibrational spectra, and relative energies of HBrO2, ClBrO2, and BrBrO2 isomers have been examined using various density functional (BLYP, SVWN, and B3LYP) methods. A comparison of the density functional results for HBrO2 isomers with singles and doubles coupled-cluster theory which incorporates a perturbational estimate of the effects of connected triples excitation [CCSD(T)] shows that B3LYP results are in excellent agreement in predicting the geometries, vibrational spectra, and relative energies and should yield reasonable results for ClBrO2 and BrBrO2 isomers. The results also show interesting trends for HBrO2, ClBrO2, and BrBrO2 isomers. The peroxide form, XOOBr, is found to be the lowest energy structure among the isomers. The heats of formation at 0 K for HOOBr, ClOOBr, and BrOOBr are estimated to be 8.6, 38.9, and 46.1 kcal mol-1, respectively. Increase in halogenation tends to destabilize the peroxide thermodynamically. We examine the implication for the formation of XBrO2 isomers from atmospheric cross reactions of HO x , ClO x , and BrO x species.

The pathways for the reaction between methylperoxy (CH3O2) and bromine monoxide (BrO) radicals have been examined by using the quadratic configuration interaction method. It is found that the most feasible pathway of the CH3O2+BrO reaction is the formation of CH3OOOBr as an intermediate during the reaction and its dissociation into CH2O and HOOBr. This study finds that besides CH3OOOBr, CH3OOBrO may also exist as an intermediate complex during the CH3O2+BrO reaction.

The geometries, vibrational spectra, and relative energetics of HBrO3 isomers have been examined using various ab initio and density functional [MP2, CISD, CCSD(T), and B3LYP] methods. The results show interesting trends for the HBrO3 isomers. The HOBrO2 isomer is found to be the lowest energy structure among the isomers, with an estimated heat of formation of 12.6 kcal mol-1 at 0 K. We have examined the implication of the formation of the HBrO3 isomers from the atmospheric cross-reactions of the HO2 and BrO species.

The geometries, vibrational spectra, and relative energetics of CH 3 BrO 3 isomers have been examined using the B3LYP method in conjunction with various basis sets. The CH 3 OBrO 2 isomer is found to be the lowest energy structure among the isomers, with an estimated heat of formation of 10.6 kcal mol -1 , at 0 K, as determined from G2 theory. The next lowest energy isomer is CH 3 OOOBr, which lies 5.6 kcal mol -1 above CH 3 OBrO 2 . The isomers with higher energies are CH 3 OOBrO and CH 3 BrO 3 . We have examined the implication of the formation of the CH 3 BrO 3 isomers from the atmospheric cross-reactions of the CH 3 O 2 and BrO radical species.