Transcriptional Silencing of 35S rDNA in Correlates with Cytosine Methylation in Sequence-Specific Manner.

Despite the widely accepted involvement of DNA methylation in the regulation of rDNA transcription, the relative participation of different cytosine methylation pathways is currently described only for a few model plants. Using PacBio, Bisulfite, and RNA sequencing; PCR; Southern hybridizations; and FISH, the epigenetic consequences of rDNA copy number variation were estimated in two lineages, por1 and por2, the latter with more than twice the rDNA copy numbers distributed approximately equally between NORs on chromosomes A and D. The lower rDNA content in por1 correlated with significantly reduced (>90%) sizes of both D-NORs.

Release 4.0 of the Plant rDNA Database: A Database on Plant Ribosomal DNA Loci Number, Their Position, and Organization: An Information Source for Comparative Cytogenetics.

This paper presents the latest update to the Plant rDNA database (Release 4.0), a valuable resource for researchers in the field of plant cytogenetics. The database provides information on the number, position, and arrangement of ribosomal DNA loci in plants, including angiosperms, gymnosperms, bryophytes, and pteridophytes.

Analyses of the Updated "Animal rDNA Loci Database" with an Emphasis on Its New Features.

We report on a major update to the animal rDNA loci database, which now contains cytogenetic information for 45S and 5S rDNA loci in more than 2600 and 1000 species, respectively.The data analyses show the following: (i) A high variability in 5S and 45S loci numbers, with both showing 50-fold or higher variability. However, karyotypes with an extremely high number of loci were rare, and medians generally converged to two 5S sites and two 45S rDNA sites per diploid genome.

Activity measurements and determination of nuclear decay data of Ho in the MRTDosimetry project.

Holmium-166 is a high-energy β-emitter radionuclide (~ 1.8 MeV) with a short half-life (~26.8h) that offers great potential as an alternative to Y for the treatment of liver cancer based on radioembolization.

Evolutionary trends in animal ribosomal DNA loci: introduction to a new online database.

Ribosomal DNA (rDNA) loci encoding 5S and 45S (18S-5.8S-28S) rRNAs are important components of eukaryotic chromosomes. Here, we set up the animal rDNA database containing cytogenetic information about these loci in 1343 animal species (264 families) collected from 542 publications.

Gene conversion events and variable degree of homogenization of rDNA loci in cultivars of Brassica napus.

Background And Aims: Brassica napus (AACC, 2n = 38, oilseed rape) is a relatively recent allotetraploid species derived from the putative progenitor diploid species Brassica rapa (AA, 2n = 20) and Brassica oleracea (CC, 2n = 18). To determine the influence of intensive breeding conditions on the evolution of its genome, we analysed structure and copy number of rDNA in 21 cultivars of B. napus, representative of genetic diversity.

Activity standardization, photon emission probabilities and half-life measurements of (177)Lu.

Activity standardization of (177)Lu and measurement of two nuclear parameters were done. Activity standardization of (177)Lu was done utilizing the 4πβ-γ coincidence method with a combined standard uncertainty of 0.28%.

Activity standardization of ¹³⁴Cs and ¹³⁷Cs.

The paper presents the results from a primary standardization of (137)Cs using two independent methods - efficiency tracing using PC-NaI coincidence and the TDCR method. The nuclides (60)Co and (134)Cs were used as the tracers. Primary standardization of the (134)Cs is also discussed.

Standardisation of ⁶⁴Cu using a software coincidence counting system.

The activity of the radionuclide (64)Cu was determined by the efficiency extrapolation method applied to 4π(PC)-γ coincidence counting. The standardisation was performed by software coincidence counting-a digital method for primary activity measurement that simplifies the setting of optimal coincidence parameters. The γ-ray-energy window, characterised by identical gamma detection efficiency related to the sum of EC and to the sum of beta decay branches, was found.

Activity standardisation of 45Ca and 204Tl using the new TDCR system at CMI.

A new triple-to-double coincidence ratio (TDCR) system has been established at CMI as an additional technique for primary activity standardisation. Details of the detectors and the electronics are given. Construction of the optical chamber was validated using measurement of a (3)H standard-the efficiency achieved with Ultima Gold was 58%.

International exercise on 124Sb photon emission intensities determination.

An international exercise, registered as EUROMET project no. 907, was launched to measure both the activity of a solution of (124)Sb and the photon emission intensities of its decay. The same solution was sent by LNE-LNHB to eight participating laboratories, six of which sent results for photon emission intensities both in absolute and in relative terms.

International exercise on 124Sb activity measurements.

An international exercise, registered as EUROMET project no. 907, was launched to measure both the activity of a solution of (124)Sb and the photon emission intensities of its decay. The same solution was sent by LNE-LNHB to eight participating laboratories.

Standardisation of 124SB and 152EU using software coincidence counting system.

Activities of the radionuclides (124)Sb and (152)Eu were determined by the efficiency extrapolation method applied to 4pi(PC)-gamma coincidence counting. The (124)Sb sources were prepared from a solution with the chemical form of 50 microg g(-1) SbCl(3) in 2 M HCl. To inhibit the volatility of antimony chlorides, the sources were slowly dried in a H(2)S atmosphere with relative humidity of 76% for about 48 h.

Application of "wet" extrapolation method for activity standardisation of electron capture radionuclides.

The activity of electron capture radionuclides is usually determined by 4pi(proportional counter, PC)-gamma coincidence counting. The corrections necessary for the final activity value calculation are obtained by an extrapolation method. Variation of the PC detection efficiency can be achieved through different methods, e.

Standardisation of (56)Co and (57)Co using software coincidence counting system.

Activities of the radionuclides (56)Co and (57)Co were determined by the efficiency extrapolation method applied to 4pi(PC)-gamma coincidence counting. Solutions of (56)Co usually contain a significant amount of (57)Co and (58)Co, so the measured activity of (56)Co requires correction. When the conventional coincidence method is used for (56)Co standardisation, the corrections are derived from the dependence of Proportional Counter (PC) detection efficiencies for (57)Co and (56)Co measured using sources with mixture of (56)Co and (57)Co, which is complicated.

Standardisation of 54Mn and 65Zn using a software coincidence counting system.

The activities of 54Mn and 65Zn have been determined by 4pi(PC)-gamma coincidence counting, with efficiency variation performed by the conventional method of altering the self-absorption in the sources as well as by the computer discrimination method. The standardisation of 65Zn presents some complications requiring optimisation of the gamma-ray energy window settings to achieve a linear efficiency-extrapolation curve. Determination of these optimal settings by the conventional coincidence method is a tedious task.

Application of pulse mixing method in software coincidence counting.

In recent years the software coincidence counting system, designed for absolute activity measurement, has been developed in the Czech Metrology Institute. In this system a true coincidence count rate is calculated from the records of time and amplitude data of individual pulses and may be determined by two different methods. The first one uses a coincidence resolving time, in a manner similar to a classical coincidence measurement.

Software coincidence counting.

A system designed for absolute activity measurement is described using a digital method. The system is based on data recording from a coincidence measurement and subsequent software processing of the data records. The data acquisition device collects amplitudes of individual pulses from analogue-to-digital converters and supplies them with time information.