Physical structure of gene-sized chromatin from the protozoan Oxytricha

• Published in: Nucleic acids research Vol. 12; no. 7; pp. 3201 - 3217
• Main Authors: Butler, A.P., Laughlin, T.J., Cadilla, C.L., Henry, J.M., Olins, D.E.
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 11.04.1984
• Subjects: Animals; Biological and medical sciences; Chickens; Chromatin - analysis; Chromatin - ultrastructure; Chromatin. Chromosome; Circular Dichroism; DNA - analysis; Electrophoresis, Polyacrylamide Gel; Erythrocytes - analysis; Eukaryota - analysis; Fundamental and applied biological sciences. Psychology; Histones - analysis; Kinetics; Molecular and cellular biology; Molecular genetics; Nucleic Acid Conformation; Oxytricha; Oxytricha nova; Protein Conformation; Species Specificity; Transcription, Genetic; Protozoa; Chromatin; Molecular structure; Transcription; Nucleosome; Oxytricha; Thermal denaturation; Activation; Circular dichroism; Macronucleus; Micronucleus; Enzymatic digestion; Histone H1; Physical structure
• ISSN: 0305-1048; 1362-4962
• DOI: 10.1093/nar/12.7.3201

Oxytricha nova is a hypotrichous ciliate containing a transcriptionally active macronucleus and a transcriptionally inactive micronucleus. Two-dimensional gel electrophores is shows that macronuclei contain a normal complement of inner histones. However, despite extensive efforts, no classical H1-like protein has been detected. Micrococcal nuclease digestion indicates a nucleosome repeat length of approximately 220 bp for macronuclear chromatin. Thermal denaturation profiles of macronuclear chromatin in 0.2 mM EDTA display four transitions at about 46, 57, 64, and 79°C. The lowest of these shifts to higher temperature as the ionic strength is raised to 3-5 mM Na phosohate. These results are consistent with the absence of H1 and a nucleosome repeat of 220–230 bp. Circular dichroism (CD) results aqree with these findings. By contrast, micronuclear chromatin displays a much smaller premelt and a more suppressed DNA CD signal at 285 nm, consistent with a micronuclear chromatin repeat of 165–185 bp as determined by micrococcal nuclease digestion.