RESUMO
The budding yeast RENT complex, consisting of at least three proteins (Net1, Cdc14, Sir2), is anchored to the nucleolus by Net1. RENT controls mitotic exit, nucleolar silencing, and nucleolar localization of Nop1. Here, we report two new functions of Net1. First, Net1 directly binds Pol I and stimulates rRNA synthesis both in vitro and in vivo. Second, Net1 modulates nucleolar structure by regulating rDNA morphology and proper localization of multiple nucleolar antigens, including Pol I. Importantly, we show that the nucleolar and previously described cell cycle functions of the RENT complex can be uncoupled by a dominant mutant allele of CDC14. The independent functions of Net1 link a key event in the cell cycle to nucleolar processes that are fundamental to cell growth.
Assuntos
Nucléolo Celular/fisiologia , Mitose/fisiologia , Proteínas Nucleares/metabolismo , Proteínas Pol1 do Complexo de Iniciação de Transcrição , Proteínas Tirosina Fosfatases , RNA Polimerase I/metabolismo , Ribonucleoproteínas Nucleolares Pequenas , Proteínas de Saccharomyces cerevisiae , Proteínas Reguladoras de Informação Silenciosa de Saccharomyces cerevisiae , Transcrição Gênica , Animais , Northern Blotting , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Nucléolo Celular/ultraestrutura , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Histona Desacetilases/genética , Histona Desacetilases/metabolismo , Hibridização in Situ Fluorescente , Microscopia de Fluorescência , Proteínas Nucleares/genética , Conformação de Ácido Nucleico , Fenótipo , RNA Ribossômico/biossíntese , RNA Ribossômico/genética , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Saccharomyces cerevisiae/fisiologia , Sirtuína 2 , Sirtuínas , Esporos Fúngicos/fisiologia , Temperatura , Transativadores/genética , Transativadores/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
The influence of pH, tonicity, preservatives, polymers and instilled drop size on the disposition of sodium cromoglycate, an agent used in the prophylaxis of vernal keratoconjunctivitis, in the tear chamber of the albino rabbit eye has been examined. Radiotracer techniques were used throughout. The initial decline in concentration in the tear chamber was found to be unaffected by the presence of preservatives, pH, and tonicity over the ranges studied. However, significant increases in the residence time of sodium cromoglycate in the precorneal area were noted when a smaller instilled drop size was used and when 5% polyvinyl alcohol (PVA) was added to the aqueous vehicle. Tissue uptake was found to be greatest in the conjunctiva, followed by the cornea, the iris-ciliary body and the aqueous humor. In both the conjunctiva and the cornea, the addition of 5% PVA produced an elevation in the peak concentration of sodium cromoglycate and an increase in the time at which the peak concentration was achieved, indicating improved drug delivery to these sites.
Assuntos
Cromolina Sódica/metabolismo , Olho/metabolismo , Animais , Química Farmacêutica , Cromolina Sódica/administração & dosagem , Excipientes , Concentração de Íons de Hidrogênio , Masculino , Soluções Oftálmicas , Conservantes Farmacêuticos , Coelhos , Fatores de Tempo , ViscosidadeRESUMO
Being the major pathway by which topically applied ophthalmic drugs enter the eye, the cornea can control the amount of active drug ultimately absorbed by offering resistance to drug permeation and by metabolizing the drug during permeation. This research seeks to determine the esterase activity in the cornea and two of its component layers--epithelium and stroma-endothelium--so as to anticipate the extent to which drugs containing ester linkages will be metabolized during transport. This has been achieved by incubating corneal homogenates of albino and pigmented rabbits of various age groups with alpha-naphthyl acetate, the model substrate, and monitoring the fluorescence intensity due to alpha-naphthol as a function of time. The results indicate that: (1) esterase activity in the epithelium is approximately twice that in the stroma-endothelium; (2) esterase activity in the intact cornea is linearly related to those in the epithelium and the stroma-endothelium; and (3) the esterase activity in the cornea and its component layers varies with rabbit's age and strain. According to these results the bulk of esterase-mediated hydrolysis is expected to take place in the epithelium, so that the residence time of a drug in this tissue can have a significant impact on its ocular bioavailability.
