Biomaterial Database

A quantitative electron-microscope analysis of chromatin from Xenopus laevis lampbrush chromosomes. 1979

R S Hill

The morphology of the DNP axis and RNP transcripts from Xenopus laevis lampbrush chromosomes has been analysed using a modified Miller spreading technique. Two basictypes of chromatin have been distinguished. (1) Discrete portions of DNP exhibiting high levels of transcriptive activity, with clear initiation and termination points (transcription units). Interspersed with the units are sequences with little or no transcriptive activity (spacer DNP). The combination of transcription unit plus spacer DNP is normally repeared to form a transcriptive array. (2) large aggregates of loosely packed, mainly transcriptively inactive regions (chromomeric DNP). Where the DNP axis is not obscured by tightly packed polymerases it has regular beaded appearance, both in the transcriptive arrays and in chromomeric DNP. The beads are 17-20 nm in diameter and have packing densities of about 40 beads per micron of chromatin in preparations from young females not stimulated by human chorionic gonodotrophin. Most transcription units have polymerase packing densities of 13-20 polymerases per micron, but in some cases the density is much lower (less than 10 polymerases /micron). The lateral RNP transcripts in most units have a complex, bushlike appearance, the axis being beaded and folded to form circles and branches.

UI	MeSH Term	Description	Entries
D008854	Microscopy, Electron	Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.	Electron Microscopy
D009690	Nucleic Acid Conformation	The spatial arrangement of the atoms of a nucleic acid or polynucleotide that results in its characteristic 3-dimensional shape.	DNA Conformation,RNA Conformation,Conformation, DNA,Conformation, Nucleic Acid,Conformation, RNA,Conformations, DNA,Conformations, Nucleic Acid,Conformations, RNA,DNA Conformations,Nucleic Acid Conformations,RNA Conformations
D002843	Chromatin	The material of CHROMOSOMES. It is a complex of DNA; HISTONES; and nonhistone proteins (CHROMOSOMAL PROTEINS, NON-HISTONE) found within the nucleus of a cell.	Chromatins
D002875	Chromosomes	In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. (From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)	Chromosome
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D012261	Ribonucleoproteins	Complexes of RNA-binding proteins with ribonucleic acids (RNA).	Ribonucleoprotein
D014158	Transcription, Genetic	The biosynthesis of RNA carried out on a template of DNA. The biosynthesis of DNA from an RNA template is called REVERSE TRANSCRIPTION.	Genetic Transcription
D014981	Xenopus	An aquatic genus of the family, Pipidae, occurring in Africa and distinguished by having black horny claws on three inner hind toes.