Chromatin from TLT hepatoma cells, mouse liver cells, and mouse brain cells was fractionated by differential centrifugation into a pellet, enriched with heterochromatin, and a supernatant, enriched with euchromatin. The pellet was found to contain more than twice as much of a particular species of chromatin-associated RNA per milligram chromatin DNA as did the supernatant. This chromatin-associated RNA was also found to be associated with the transcriptionally inactive chromatin of mature avian erythrocytes. Bull sperm, whose genome is known to be completely inactive, was used as the source in the preparation of sperm heads. Bull sperm head RNA appeared to consist of a single, low molecular weight species which migrated on polyacrylamide gels at a rate just slightly slower than the aforementioned chromatin-associated RNA. The results are interpreted as indicating that this chromatin-associated RNA is more prevalently associated with the heterochromatic fraction of chromatin. It is postulated that this chromatin-associated RNA might constitute a structural component of heterochromatin.

cells among the images under f of the vertices of tj +1 is exactly r + 1, it is easily verified that f(btjr+l) contains exactly two non-degenerate r-simplexes of opposite orientations, so that f(atjr+1) = 0 + degenerate r-simplexes. If the number is less than r + 1, there are no nondegenerate r-simplexes in f(bt j +1). Hence, the only cases in which f(btfr+l) $ 0, when degenerate r-simplexes are dropped, are, those in which the r + 2 vertices of tTr+l are mapped onto the r + 2 vertices of sr+'.Suppose that this happens for x of the tjT+' with orientation preserved and for y with orientation reversed. Then Ef(btTr+1) = (x -y)(sor + sir + Sr+1), and, as in the proof for the case n = 1, we infer that x -y = 1. This completes the proof. Considerable evidence has been accumulated to show that ribonucleoprotein particles (ribosomes) provide sites for protein synthesis in animal cells.' Studies of the incorporation of radioactive tracers by Escherichia coli also indicated that the ribosomes of bacteria are active in protein synthesis (McQuillen, Roberts, and Britten2). These authors showed that in growing bacteria, a quantity of material roughly equal to the protein synthesized in three seconds was transiently associated with the ribosomes before being released to the soluble protein fraction of the cell. Since the rate of protein synthesis in E. coli is about 0.02 per cent per second, 0.06 per cent of any partictlar protein might be expected to be found transiently associated with the ribosomes. A series of experiments was started to determine whether fl-galactosidase showed the same transient association with ribosomes as was indicated for proteins in general. The first experiments showed that a small fraction of the enzyme was bound to the ribosomes, and it is the purpose of the present paper to describe some of the properties of this ribosome-associated enzyme. Furthermore, the results suggest a general procedure for isolating specific ribosomes.Materials and Methods.-E. coli strains: Three strains of E. coli differing in their 8-galactosidase-synthesizing properties were used, namely ML 30 (inducible), ML 308 (constitutive), and W2214 (absolute negative).Growth conditions: Cells were grown at 37°C in a vigorously aerated synthetic medium (C) of the following composition: 2 g NH4Cl, 6 g Na2HPO4, 3 g KH2PO4, 3 g NaCl, 0.01 g Mg as MgCl2, 0.026 g S as Na2SO4, 900 ml H20, and 10 ml. of 10 per cent maltose.Enzyme induction and assay: Thiomethyl-,3-D-galactoside (TMG) or thioisopropyl-fl-D-galactoside (TIPG) at 5 X 10-4 M were used as inducers of ft-galactosidase synthesis. Assays of d-galactosidase on ribosomal preparations were performed with the following mixture buffered at pH 7.4; 0.0027 M ortho-nitrophenyl-P-D-galactoside (ONPG), 0.05 M NaCl, 0.01 M trishydroxymethylaminomethane

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