Site distribution of malignant melanoma.

In a continuous series of 300 patients with cutaneous malignant melanoma the site of the primary lesion was recorded, and incidence rates per unit area of skin were calculated. These rates were high for the face, back and upper arm and low for the abdomen, buttocks, forearm and hand for both sexes. Rates for the leg were high for the women but low for the men. Tumours on the back were evenly distributed among the men but occurred less frequently on the lower back among the women. In general, sites that were usually covered by clothing had lower rates than those usually exposed, with the exception of the forearms and hands. No relation was seen between tumour site and age, sex, depth of invasion or month of diagnosis. Superficial spreading and nodular melanomas did not differ in their site distribution. Incidence rates per unit area at different ages were estimated for sites grouped by their degree of usual exposure: while the rates for unexposed sites were low, those for usually or intermittently exposed sites were higher and similar to each other.     

Site directed mutagenesis: a tool for enzyme mechanism dissection.

Protein engineering has become the principle means of examining the active site of an enzyme to identify and quantify the roles of specific residues in ligand binding, specificity and catalysis. Site-specific mutagenesis has extended our knowledge gained from X-ray crystallography, and has provided striking proof that the intricate active-site geometry is supported by the remainder of the protein infrastructure for maximum catalytic efficiency.     

Site 48SH312:

Abstract

Site 48SH312 is part of an Early Middle Period complex in which at least part of the economy was oriented toward small-scale trapping of bison, utilizing the natural badland topography of the Powder River Basin. Further work is necessary to determine more of the economy as well as temporal and spatial aspects of the complex.     

Retroviral integration: Site matters

Here, we review genomic target site selection during retroviral integration as a multistep process in which specific biases are introduced at each level. The first asymmetries are introduced when the virus takes a specific route into the nucleus. Next, by co‐opting distinct host cofactors, the integration machinery is guided to particular chromatin contexts. As the viral integrase captures a local target nucleosome, specific contacts introduce fine‐grained biases in the integration site distribution. In vivo, the established population of proviruses is subject to both positive and negative selection, thereby continuously reshaping the integration site distribution. By affecting stochastic proviral expression as well as the mutagenic potential of the virus, integration site choice may be an inherent part of the evolutionary strategies used by different retroviruses to maximise reproductive success.     

Site directed in-vitro assembly of nucleosomes.

An in-vitro system is described allowing for the assembly of nucleosomes on preselected sites of a cloned tRNA gene. The system consists of a soluble nucleoprotein fraction, a histone source, and circular DNA containing a single stranded stretch (sssDNA). Nucleosomes assemble on the sssDNA, if the three components are incubated as a highly concentrated solution in the presence of the four deoxyribonucleotidetriphosphates and of ATP. The single stranded stretch is rendered double stranded during incubation. The middle axis of one assembled nucleosome always coincides roughly with the midpoint of the original single stranded DNA stretch.     

Site specific endonuclease from Fusobacterium nucleatum.

Four different isolates of Fusobacterium nucleatum (A,C,D and E) contain restriction endonucleases of differing specificity. Whilst many of the endonucleases are isochizomers of known enzymes, two novel activities are Fnu DII which recognizes and cleaves the sequence 5'-CGCT-3'/3'-GCGC-5' AND Fnu EI which recognizes and cleaves the sequence 5'-GATC-3'/3'-CTAG-5' irrespective of the extent of methylation of the adenine residues.     

Site specific enzymatic cleavage of RNA.

The hybridization of a DNA oligonucleotide a specific tetramer or longer) will direct a cleavage by RNase H (EC 3.1.4.34) to a specific site in RNA. The resulting fragments can then be labeled at their 5' or 3' ends, purified, and sequenced directly. This procedure is demonstrated with two RNA molecules of known sequence: 5.8S rRNA from yeast (158 nucleotides) and satellite tobacco necrosis virus (STNV) RNA (1240 nucleotides).