Protease activity associated with HeLa cell ribosomes

Localization of a multi-catalytic, high-molecular mass proteinase in the nuclei of muscle cells

A multi-catalytic protease in muscle cells was uniquely localized to the nucleus of muscle cells, both in cell culture and in sections of muscle tissue. Although no specific substructure of the nucleus could be identified as the site of the enzyme by immunocytochemical techniques, the enzyme was nevertheless present in all muscle cell nuclei. It appears that MCP is a useful marker for nuclei found specifically in muscle tissue.

The breakdown of Tetrahymena ribosomes in vivo. The effects of inhibitors

1. When Tetrahymena were deprived of nutrients 50% of the polysomes disaggregated within 20 min and 20% of the total RNA broke down in 2 h. Ribosomal RNA accounted for 75% of the RNA breakdown. 2. RNA labelled by a long incubation with [14C]uridine was stable in growing cells and in the presence of actinomycin D, but broke down at the same rate as bulk RNA in starved cells. 3. The following substances inhibited the loss of RNA during starvation: cycloheximide (which inhibited both polysome disaggregation and protein synthesis), inhibitors of energy metabolism and puromycin (all of which caused polysome disaggregation and inhibited protein synthesis), and chloroquine and 7-amino-1-chloro-3-L-tosylamidoheptan-2-one ('TLCK') (neither of which affected polysomes or protein synthesis). 4. Starvation appears to activate a ribosome degradation mechanism that may involve lysosomal and non-lysosomal enzymes.

The ribosomal serine proteinase, cathepsin R. Occurrence in rat-liver ribosomes in a cryptic form

Ribosomes have been shown to contain a proteolytic activity, characterized as an endopeptidase with serine in the active center. The enzyme has been given the name cathepsin R, following the recommendations of Barrett et al. (in a publication from the Cold Spring Harbor Laboratory, New York) for naming new proteinases. The present paper contains evidence that cathepsin R in rat liver ribosomes is present in a cryptic form. Upon dissociation of ribosomes to subunits (and to minor extent also by 0.5 M KC1 washes), the cryptic proteinase is released. Activation of the released cathepsin R is effected by equilibration with 2 M NaC1/0.05 M sodium acetate, pH 4.8. The molecular weight of free cathepsin R is 25 000-30 000.

Characterization of native 40 S particles from Krebs II mouse ascites tumor cells: resolution, nomenclature and molecular weights of the nonribosomal proteins

Native 40 S particles from Krebs II mouse ascites tumor cells were isolated on a large scale. A nonribosomal protein moiety of about 30 proteins could be removed from the ribosomal particles by treatment with 250 mM KCl. These proteins were analysed by two-dimensional polyacrylamide gel electrophoresis and turned out to be mostly acidic in nature. The molecular weights of about 17 proteins were determined by three-dimensional gel electrophoresis. Radioactively labelled nonribosomal protein spots were excised from two-dimensional gel electrophoresis. Radioactively labelled nonribosomal protein spots were excised from two-dimensional gels and transferred directly or after electrodialysis onto the third dimension gel. The proteins fell into a molecular weight range from about 20,000 to 300,000.

Differences in electrophoretic behaviour of eight ribosomal proteins from rat and rabbit tissues and evidence for proteolytic action on liver proteins

Divergence exists between eight ribosomal proteins of rat and rabbit. This is the first time such a divergence has been precisely demonstrated among mammals. In addition, a proteolytic activity, giving the appearance of modified proteins, is observed in the liver of both species but not in rabbit reticulocytes. These results were made possible by a recently developed method. Ribosomal proteins were compared by two-dimensional polyacrylamide gel electrophoresis in four different but related systems. The precise position of each individual protein was established in each of the four systems. Certain ribosomal proteins from different tissues, seemingly identical in one system were found to be different in other systems. Significant differences occurred between proteins of each ribosomal subunit from the two different species. Variation between reticulocyte and liver ribosomal proteins of the rabbit were minor. Several liver proteins of both species change position or disappear and apparently new proteins appear, if appropriate steps are not taken to prevent proteolysis. Differences in behavior of three small subunit and five large subunit proteins are attributable to an evolutionary divergence between the two species.

The localization of an intracellular membrane-bound proteinase from rat liver

To localize the membrane-bound, histone-degrading proteinase, which was previously isolated from the mitochondrial fraction, nuclei, mitochondria, lysosomes, peroxisomes, smooth and rough endoplasmic reticulum, ribosomes and plasma membranes were prepared from a rat liver homogenate according to established methods and characterized by marker enzyme activities. The isolated subcellular fractions were treated with digitonin, and subjected to a discontinuous sucrose gradient centrifugation. The material, which sedimented through 1.74 M surcrose was analyzed in respect to the various marker enzymes and for proteolytic activity. Proteinase activity was found in the material obtained after digitonin treatment and step gradient centrifugation of mitochondria. This finding shows the occurrence of a proteinase in mitochondria; After fractionation of mitochondria into outer and inner membrane, intermembrane fraction and matrix, the proteinase could be localized exclusively in the inner mitochondrial membrane. A possible physiological function of the enzyme during the biosynthesis of inner membrane constituents is discussed.