摘要:

AbstractNon‐histone chromosomal proteins are phosphorylated and dephosphorylated within the intact nucleus by two independent sets of reactions, a protein kinase reaction which transfers the terminal phosphate group of a variety of nucleoside and deoxynucleoside triphosphates to serine and threonine residues in the proteins, and a phosphatase reaction which cleaves these phosphoserine and phosphothreonine bonds and releases inorganic phosphate. Several lines of evidence are consistent with the hypothesis that the phosphorylation and dephosphorylation of these proteins is involved in gene control mechanisms, including the findings that phosphorylated non‐histone proteins are highly heterogeneous and their phosphorylation patterns are tissue specific, changes in their phosphorylation correlate with changes in chromatin structure and gene activity, addition of phosphorylated non‐histone proteins increases RNA synthesis in vitro, and phosphorylated non‐histone proteins bind specifically to DNA.Cyclic AMP has both stimulatory and inhibitory properties on non‐histone protein phosphorylation, depending on the enzyme fraction and substrate employed. A specific protein component whose phosphorylation is inhibited by cyclic AMP has been found to be associated with RNA polymerase. The cyclic AMP‐induced decrease in the phosphorylation of this protein correlates with an enhancement of RNA synthesis in vitro. These results suggest that both phosphorylation and dephosphorylation of chromatin‐associated proteins may be involved in the control of

ISSN:0021-9541    

DOI:10.1002/jcp.1040850412

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractGlobin gene switching in sheep and goats has been used as a model system for examining gene expression in differentiating red blood cells. Sheep and goats switch from the synthesis of hemoglobin A to hemoglobin C in response to erythropoietin. The regulatory mechanism producing this switch in hemoglobin types could occur at the cellular, nuclear, or cytoplasmic level. Evidence is presented which suggests that regulation is occurring, in fact, at the nuclear level. Sheep and goat erythroid colonies have been grown in plasma clot culture in order to study the synthesis of individual globin chains. Erythropoietin is required for colony formation. The switch from hemoglobin A to hemoglobin C synthesis requires not only colony formation but also a higher concentration of erythropoietin than is required just for the production of colonies. A cell‐free transcriptional system using bone marrow chromatin and mammalian DNA‐dependent RNA polymerase has been developed in order to examine the nuclear control mechanisms in more det

ISSN:0021-9541    

DOI:10.1002/jcp.1040850413

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractCell differentiation during spermatogenesis in the rat has been analyzed in terms of the formation of specific “marker” enzymes. Hyaluronidase and other acrosomal enzymes are formed in spermatids according to a highly predictable time schedule which may be termed a “molecular biological clock”. The acrosomal enzymes β‐galactosidase and N‐acetyl‐β‐glucosaminidase exist as isoenzyme forms distinct from enzymes with similar substrate specificities in the lysosomes of precursor cells. Differentiation of spermatids thus involves the loss of gene expression for lysosomal enzymes and the activation of genes for acrosomal isoenzymes. Spermatogenesis is characterized by the sequential loss of expression of many genes, as evidenced by the loss of β‐glucuronidase in the differentiation of spermatogonia to spermatocytes, and the loss of uridine diphosphatase activity in the differentiation of spermatocytes to spermatids. The apparent absence of ornithine decarboxylase activity from spermatids suggests a dependence of these cells upon Sertoli cells for the provision of putrescine and/or spermidine. Such biochemical cooperativity among germinal cells may be necessary as the genes of spermatids are repressed and late spermatids become metabolically inactive. Spermatogenesis is also characterized by changes in the cellular content and rates of synthesis and phosphorylation of specific acidic chromatin proteins. It is hypothesized that these proteins may participate in the activation or repression of genes du

ISSN:0021-9541    

DOI:10.1002/jcp.1040850414

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

ISSN:0021-9541    

DOI:10.1002/jcp.1040850401

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY