Identification of thymostimulin secreting cells in calf thymus by immunoperoxidase method

An anti- thymostimulin (TS) serum was tested on calf thymus to study the localization of the hormonal factor. The immunoperoxidase method was applied to tissue fixed in Bouin's fluid and embedded in paraffin, or to tissue fixed in paraformaldehyde and embedded in Epon for semi-thin sections. Immuno-reactivity was shown, with DAB- Fluka , in reticulo-epithelial cells in the medulla, and between the cortex and the medulla, while with DAB-Sigma reactivity was found in the cortex as well. The external cells of Hassall's corpuscles were also reactive. Myoid cells were not reactive. In semi-thin sections a weak reactivity was noted at the periphery of a few lymphocytes. Comparison with the localization of other thymic factors, and the possibility of a functional cycle of the epithelial cells synthesizing one or more factors are discussed.     

Modification of histone binding in calf thymus chromatin by protamine.

When calf thymus chromatin is incubated with protamine, the protein binds to DNA, forming a chromatin-protamine complex. The binding reaches a saturating level at the weight ratio of protamine to DNA of approximately 0.5. Although the saturated binding of protamine to DNA does not cause major displacement of histones from calf thymus chromatin, examination of the dissociation profiles by salt in combination with urea of protamine-treated chromatin shows that the histone-DNA interactions are markedly altered by such binding. The dissociation of histones from the chromatin-protamine complex requires less NaCl but the same concentration of urea as that for untreated chromatin, suggesting that the electorstatic interactions between the histones and DNA are decreased as a result of protamine binding. When protamine concentration is increased beyond that required for saturated binding to DNA during in vitro exposure of calf thymus chromatin to protamine, lysine-rich histone is completely displaced.     

Enzymatic demethylation of calf thymus histones

Enzymatic demethylation of ε-N-methyllysine residues of calf thymus histone has been investigated. Kidney contains the highest enzyme activity among the rat organs tested, and the enzyme activity is associated with the nuclear and mitocondrial fractions. Formaldehyde-C-14 is the product of demethylation of enzymatically prepared histone-methyl-C-14. Evidence indicates that demethylation occurs on the intact histone molecule.     

Phosphopeptides in highly purified calf thymus DNA

Highly purified DNA obtained from calf thymus nuclei was found to cleave after reaction with a chelating agent and subsequent dialysis against 0.01 M phosphate. During the cleavage release of proteineous material into the dialysate was observed. By means of anion exchange resin column chromatography, this material was separated into 9 main fractions. Two of these fractions P1 and P5) were found to contain the amino acids phosphoserine, asp, thr, ser, glu, gly, ala, val, ile, leu, and arg, as well as metal ion complexes of phosphoserine. The complexes were dissociated by Chelex 100 treatment. The proportion of phosphoserine was much greater in P5 than in P1. P1 and P5 contained essentially no nucleotide material. All other fractions (P2, P3, P3a, P4, P5a, P6, P7, P8, P6a, P9) were found to contain ribonucleotides and deoxynucleotides. The deoxynucleotide content was about 10% of total nucleotide content. After a deionizing treatment with Chelex, the amounts of nucleotides were extensively reduced to a level corresponding to about 1 nucleotide of 10 amino acids. In separate experiments, commercial DNA (S-DNA) was ultrasonicated, and digested with pancreatic DNAase, exonuclease III, and S1 nuclease. From DEAE Sephacel chromatography of this material the fraction obtained having the highest proportion of protein aceous material was hydrolyzed with Pronase and again chromatographed on DEAE Sephacel. From this fractionation a single fraction containing deoxynucleotides and amino acids was found. The mixture obtained by hydrolysis of this fraction with snake venom diesterase and was again rechromatographed, which revealed two peaks, one corresponding to deoxynucleotide material and a second one to a mixture of 4 amino acids, phosphoserine, asp, glu, and gly. From this it was concluded that the fraction used for diesterase digestion consisted of deoxynucleotide-amino acids, with covalent diester bonds between their deoxynucleotide and amino acid portions. The results indicate that in purified S-DNA phosphopeptides are linked through covalent bonds to the terminal deoxynucleotide residues.     

Identification and separation of components of calf thymus DNA using a CsCl-netropsin density gradient

Calf thymus DNA containing satellite components of various densities was used as a model to study the effect of netropsin on the density of DNA in a CsCl gradient. The binding of netropsin resulted in a decrease in density which depended upon the quantity of netropsin added and on the average composition of the DNA. Differences in density of DNA components were higher in CsCl - netropsin gradients than in simple CsCl gradients. By use of netropsin a main band and four satellite bands could be differentiated in calf thymus DNA. Satellite DNA's were isolated using preparative CsCl - netropsin gradient centrifugation and were characterised by density and homogeneity in native and in reassociated state. Two of the satellite components, with densities of 1.722 and 1.714 g/cm³, are probably of homogenous sequence, the other two components of densities 1.709 and 1.705 g/cm³ appear to be heterogeneous.     

分析EST寻找小鼠胸腺基质细胞表达基因

网上生物信息量的膨胀导致新基因寻找手段的改变,借助mRNA差异显示技术获得的17个表达序列标签（EST）,通过对美国国家生物技术信息中心（NCBI）的非冗余序列库（NT）和小鼠EST库的BLAST同源检索,发现有4个序列与已知基因高度同源,其中的HDPs和Eps8两个基因是首次在小鼠胸腺基质细胞中发现,它们可能与T细胞在胸腺内的发育分化有关,其它EST则为新基因,本结果也为下一步新基因的克隆及功能研究提供了有益的线索。