title: Diffusible factors are responsible for differences in nuclease sensitivity among chromatins originating from different cell types.
abstract: We have examined the kinetics of nuclease digestion of chromatin from committed and uncommitted cells in experiments where the nuclei are mixed and co-digested. Cultures of the sea urchin, Arbacia punctulata, were grown to the 16-cell stage in either [3H]thymidine or [14C]thymidine and the macromere, mesomere, and micromere cell types separated. After isolation, sets of nuclei with two different blastomere types (each having different radionucleotide tagging) were mixed and co-digested with micrococcal nuclease or DNase. I. The extent of digestion was monitored by solubility in 5% perchloric acid (PCA). We find no significant differences in initial digestion rates or limit digests among the different cell types when co-digested with either nuclease. Differences in nuclease sensitivity observed when nuclei are digested separately are abolished when nuclei are probed in a mixing experiment. The results support the hypothesis that phenotypic differences in digestibility among different cell types in vitro reflect differences in chromatin-condensing factors which can diffuse between nuclei.
mesh_terms: D000818:Animals; D001757:Blastomeres / Q000166:cytology; D002250:Carbon Radioisotopes; D002455:Cell Division; D002467:Cell Nucleus / Q000648:ultrastructure; D002843:Chromatin / Q000502:physiology / Q000648:ultrastructure*; D004261:DNA Replication; D003850:Deoxyribonuclease I; D004625:Embryo, Nonmammalian / Q000166:cytology; D004706:Endodeoxyribonucleases / Q000378:metabolism*; D005260:Female; D007700:Kinetics; D008836:Micrococcal Nuclease / Q000378:metabolism*; D012617:Sea Urchins / Q000196:embryology; D013936:Thymidine / Q000378:metabolism; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D002843:Chromatin; D014316:Tritium; D004706:Endodeoxyribonucleases; D003850:Deoxyribonuclease I; D008836:Micrococcal Nuclease; D013936:Thymidine