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.

No abstract

No abstract

Micrococcal nuclease digestion of mouse TLT liver hepatoma chromatin proceeds rapidly to the point where approximately 35% of the DNA is recoverable by centrifugation of the chromatin DNA through 3M CsCl. The satellite DNA sequence content of this recoverable DNA is the same as whole chromatin DNA (10%). The 11s (penultimate digestion product) monomer, as well as intermediate multiples and relatively undigested large chromatin segments are separable on steep hlycerol gradients. The DNA isolated from these fractions also contains the normal 10% satellite DNA content. Progressive polylysine titration of chromatin followed by nuclease digestion gives anomalous recoveries of DNA but, nonetheless, the satellite sequence content titration of chromatin, followed by pronase and then nuclease digestion, again gave recoverable DNA with a satellite sequence content of 10%. These results are discussed in terms of the conclusion that nucleosome (or upsilon-body) structures are distributed in a random fashion over the genome.