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Biomedical subjects

M Noll

Publications and source records attributed to M Noll.

At least 73 records · Page 4Linked to original sources
PubMed1985

Cloning of the extra sex combs gene of Drosophila and its identification by P-element-mediated gene transfer.

A large region containing the extra sex combs (esc) gene of Drosophila has been cloned by microdissection from polytene chromosomes and chromosomal walking. Within this DNA, the segment comprising the esc gene has been narrowed down in several steps. First, a deletion of the esc gene, Df(2L)esc, defined a region of 380 kb. Then, a duplication carrying the esc gene, Dp(2;2)GYL, and a deletion not eliminating esc, Df(2L)prd, further reduced this region to 160 kb. Finally, because esc transcripts are expected to be present in follicles but absent in adult males, mapping of follicle and adult male transcripts limited the esc region to 10 kb. Rigorous proof that this DNA contained the esc gene was obtained by P-element-mediated transformation. We conclude that the 12 kb of DNA used for transformation include the esc gene as well as all flanking sequences required for its proper regulation in the female germ line.

Journal Article↗
PubMed1981

Chromatin fine structure of active and repressed genes.

Study of the structural organization of chromatin during transcription and replication may reveal important aspects of these processes. At the lowest level of organization, chromatin consists of a repeating subunit, the nucleosome (for reviews see refs 1-3). Electron microscopy indicates that the nucleosomes are arranged helically or form discrete superbeads, generating the familiar 250 A-300-A fibre. It has been suggested that this fibre is further folded into loops containing up to several hundred nucleosomes. Despite extensive study, the significance and fate of these nucleosomes remain obscure. We have used here micrococcal nuclease digestion to compare the structures of actively transcribing and inert chromatin of the genes coding for the major heat-shock protein of Drosophila melanogaster. The repressed hsp 70 genes were considerably more resistant to cleavage by micrococcal nuclease than their flanking regions and the bulk of chromatin. The active genes, previously shown to be more sensitive than the repressed genes, are also more susceptible to the nuclease than their 3'-flanking regions and bulk chromatin.

Animals↗
PubMed1980

Self-assembly of single and closely spaced nucleosome core particles.

Self-assembly of DNA with the four core histones but in the absence of H1 generates nucleosome core particles which are spaced randomly over large distances. Closely spaced core particles, however, exhibit a preferred short linkage which is not a multiple of 10 base pairs. They bind about 140 base pairs whereas apparently shorter DNA lengths per nucleosome observed after digestion with micrococcal nuclease are the result of degradation from the ends. The DNA length of one superhelical turn in the core particle is 83 +/- 4 base pairs. Single core particles may bind more DNA than closely spaced core particles but probably less than two full turns of 168 base pairs. The internal structures of single and of native core particles are very similar as judged by their amount of DNA, sedimentation coefficient, appearance in the electron microscope, and digestion with DNase I. In addition to core particles, a particle is described which sediments at 9 S and consists of 108 base pairs of DNA bound to the histone octamer. It appears to be the smallest stable "core particle" but it is not a degradation product of the 146-base-pair core particle. Digestion of end-labeled 9 S and nucleosome core particles with DNase I shows distinct differences.

Animals↗
PubMed1980

Efficient transfer of highly resolved small DNA fragments from polyacrylamide gels to DBM paper.

A procedure is described that combines high resolution of small DNA molecules (10 to 250 bases) with high transfer efficiency from polyacrylamide gels to diazobenzyloxymethyl (DBM) paper. The DNA fragments are separated electrophoretically in denaturing or nondenaturing step gels. These consist of a short gel of relatively high polyacrylamide concentration (8%) above a long gel of relatively low polyacrylamide concentration (4%). Step gels permit a high resolution of small DNA fragments in gels of sufficiently low polyacrylamide concentration from which efficient transfer to DBM paper is feasible. The combination of the step gel with a short treatment of the gel before transfer ensures a high transfer efficiency. As much as 30% and 50% of the DNA applied to nondenaturing and denaturing gels, respectively, are bound covalently to the DBM-paper. Optimal conditions for hybridization to DBM-linked DNA molecules of 30 to 250 base length are described.

DNA↗
PubMed1978

Nucleosome arcs and helices.

Crystals and other regular arrangements of nucleosome cores have been obtained and analyzed in the electron microscope. Two types of regular structures have been studied in detail, the nucleosome arcs and cylinders. The latter are composed of concentric cylindrical layers of intertwined right-handed helices of nucleosome cores. These studies lead to the following conclusions and concepts. The overall structure of the nucleosome core is a short, wedge-shaped cylinder measuring about 110 by 110 by 60 angstroms. Nucleosome cores interact primarily between top and bottom planes. Nucleosome cores exhibit large conformational variability. A pivot allowing two degrees of rotational freedom is postulated in the region of the 70th base pair to account for this property of the nucleosome.

Animals↗
PubMed1978

[Structure of interphase chromosomes].

The chromosomes are based on a structural unit, the nucleosome. It consists of a protein care and about 200 base pairs of DNA arranged on its outside in a regular way, probably as a spiral. The protein care is a histone octamer containing two copies each of the four main types of histones, H2A, H2B, H3, and H4. The shape of the nucleosome ressembles a short wedge shaped cylinder of 110 A x 110 A x 60 A. The nucleosomes are closely spaced and linked by the continuous DNA. Since the fifth histone, H1, stabilizes the interaction of adjacent nucleosomes, it is considered to be involved in the formation of higher structural orders in the chromosomes.

Chromosomes↗
PubMed1976

Differences and similarities in chromatin structure of Neurospora crassa and higher eucaryotes.

The subunit structure of Neurospora chromatin which contains a full histone complement (Goff, 1976) exhibits both differences and similarities to chromatin of higher eucaryotes. The size of the DNA per subunit is only 170 +/- 5 base pairs, as compared to 200 base pairs in higher eucaryotes. However, the internal structures of the subunits are closely related. They contain 140 base pairs of DNA that are more tightly associated with the histone core and similarly arranged on the outside of the subunit. Hence the difference in structure resides in a shorter linker region of adjacent subunits in Neurospora chromatin. This is supported by a reduced primary cutting site and a lower content of lysines in histone H1. The role of H1 and its relation to the linker region are discussed.

Animals↗
PubMed1975

Electron microscopy of defined lengths of chromatin.

Defined lengths of chromatin were prepared by brief digestion with micrococcal nuclease and fractionation in a sucrose gradient. A length containing a given number of 200 base pair repeating units appeared as the same number of 100 A beads in the electron microscope. The distance between beads within a length was small, usually less than about 20 A.

Chromatin↗