NOR Activity Research Articles

The nirQ gene, which is required for denitrification of Pseudomonas aeruginosa, can activate the RubisCO from Pseudomonas hydrogenothermophila

Two putative ATP-binding proteins encoded in the gene cluster for the Calvin cycle of Pseudomonas hydrogenothermophila ( cbbQ) and for the denitrification of Pseudomonas aeruginosa ( nirQ) have been found to be similar. The cbbQ gene has been shown to activate the RubisCO from P. hydrogenothermophila in E. coli. The nirQ was functionally substituted for cbbQ. The nirQ gene restored the anaerobic growth and the NOR activity of the nirQOP mutant of P. aeruginosa, while the cbbQ gene did not.

Age related decrease of NOR activity in bone marrow metaphase chromosomes from healthy individuals.

AIMS: To present data obtained from human bone marrow preparations from healthy individual showing that the proportion of metaphases with silver stained nucleolar organiser region (AgNOR) chromosomes is associated with...

NOR activity in hippocampal areas during the postnatal development and ageing

The silver staining of the nucleolar organizer regions (Ag-NORs) was used in order to estimate the biosynthetic activity of three hippocampal areas (dentate gyrus, CA1 and CA3) during postnatal development and ageing. 32 Wistar rats were used and 4 groups were formed according to the age of the animals (14, 21, 90 days and 23 months). Several Ag-NOR parameters such as mean Ag-NOR area and the ratio between Ag-NOR and nuclear areas per neuronal cell were quantified using an image analysis system. High values of these parameters are associated with a high rate of rRNA transcription. In this way, the neural biosynthetic activity in all regions studied decreased as the older ages are reached. Differences between areas are shown with the dentate gyrus and CA1 areas decreasing faster. The different activity among these areas is discussed, taking into account the particular affect on these areas of some injuries and the ageing process. Our results support the hypothesis of NOR loss as a main cause of ageing as reported by other authors.

Mutational analysis of the nor gene cluster which encodes nitric-oxide reductase from Paracoccus denitrificans.

The genes that encode the hc-type nitric-oxide reductase from Paracoccus denitrificans have been identified. They are part of a cluster of six genes (norCBQDEF) and are found near the gene cluster that encodes the cd1-type nitrite reductase, which was identified earlier [de Boer, A. P. N., Reijnders, W. N. M., Kuenen, J. G., Stouthamer, A. H. & van Spanning, R. J. M. (1994) Isolation, sequencing and mutational analysis of a gene cluster involved in nitrite reduction in Paracoccus denitrificans, Antonie Leeu wenhoek 66, 111-127]. norC and norB encode the cytochrome-c-containing subunit II and cytochrome b-containing subunit I of nitric-oxide reductase (NO reductase), respectively. norQ encodes a protein with an ATP-binding motif and has high similarity to NirQ from Pseudomonas stutzeri and Pseudomonas aeruginosa and CbbQ from Pseudomonas hydrogenothermophila. norE encodes a protein with five putative transmembrane alpha-helices and has similarity to CoxIII, the third subunit of the aa3-type cytochrome-c oxidases. norF encodes a small protein with two putative transmembrane alpha-helices. Mutagenesis of norC, norB, norQ and norD resulted in cells unable to grow anaerobically. Nitrite reductase and NO reductase (with succinate or ascorbate as substrates) and nitrous oxide reductase (with succinate as substrate) activities were not detected in these mutant strains. Nitrite extrusion was detected in the medium, indicating that nitrate reductase was active. The norQ and norD mutant strains retained about 16% and 23% of the wild-type level of NorC, respectively. The norE and norF mutant strains had specific growth rates and NorC contents similar to those of the wild-type strain, but had reduced NOR and NIR activities, indicating that their gene products are involved in regulation of enzyme activity. Mutant strains containing the norCBQDEF region on the broad-host-range vector pEG400 were able to grow anaerobically, although at a lower specific growth rate and with lower NOR activity compared with the wild-type strain.

Multiplication of 28S rDNA and NOR activity in chromosome evolution among ants of the Myrmecia pilosula species complex

Multiplication of 28S rDNA and NOR activity in chromosome evolution among ants of the Myrmecia pilosula species complex

Multiplication of 28S rDNA and NOR activity in chromosome evolution among ants of the Myrmecia pilosula species complex.

Chromosomal localization of rDNA in samples of five taxa of the Mymecia pilosula species complex (Hymenoptera: Formicidae: Myrmeciinae) with 2n = 3 (M. croslandi), 8 (M. imaii), 10 (M. banksi), 18 (M. haskinsorum), and 27 (M. pilosula) was carried out by fluorescence in situ hybridization (FISH) using cloned M. croslandi rDNA (pMc.r2) including the coding region for 28S rRNA. Results show that (1) the 28S rDNA in the genome of these ants is repetitive and is localized in pericentromeric C-bands, (2) the number of chromosomes carrying rDNA is two in M. croslandi, M. imaii and M. banksi, six in M. haskinsorum and ten in M. pilosula, and (3) only one or two clusters of rRNA genes generate nucleoli in each species. We suggest that the rDNA in the ancestral stock of the M. pilosula complex was localized originally in a pericentromeric C-band, and multiplied by chance with time during saltatory increases in C-banding following episodes of centric fission. Most rDNA multiplied on various chromosomes seems to be inactivated and eliminated from the genome, together with C-bands, by AM-inversion or centric fusion, with the remnant rDNAs dispersed in the genome by centric fission and AM-inversion.

Occurrence of macro B chromosomes in Astyanax scabripinnis paranae (Pisces, Characiformes, Characidae)

B chromosomes occur in several Neotropical fish species. Cytogenetic analysis of 27 specimens (15 females and 12 males) of Astyanax scabripinnis paranae from the Araqua river (a small headwater tributary of the Tiete river) shows that this population has 2n=50 chromosomes (4M+30 SM+4ST+12A), two chromosome pairs with NORs and conspicuous C-band positive blocks in the terminal position of the long arm of four chromosome pairs. In this population, eight females presented 2n=51 chromosomes and the extra chromosome was a large metacentric similar in size and morphology to the first chromosome pair in the karotype. This accessory chromosome is entirely heterochromatic in C-banded metaphases and shows a late replication pattern evidenced by BrdU incorporation. There was no significant correlation between the presence of B chromosomes and increased NOR activity at the P>0.05 level. Some aspects related to these B chromosomes are discussed.

Ag-NOR chromosome variability has been investigated in RbMus musculus domesticus populations as well as 40 all acrocentric ones

Results indicate high variability of the number of NORs active in both populations. Comparison between populations reveals differences both in the number of the more frequently observed active NORs and in the maximum number of active NORs. Ag-NORs present on Rb metacentric chromosomes are found to be less active than those carried on acrocentrics. It is postulated that centric fusions play a negative role with regard to NOR activity or to the characteristics enabling NORs to be observed.

NOR activity interaction among the chromosomes of common rabbit: a statistical analysis

SUMMARYA statistical analysis on NOR activity in domestic rabbit is performed in the present report, from the data obtained in the study of 2,550 metaphases stained by the Ag-I methodology. Chromosome pair number 20 is the most active one, followed by pairs 16,13 and 21. The existence of compensations between the activity levels of the nucleolar chromosomes is evidenced.

Chromosome banding analysis of a new stemline of hypodiploid Hirosaki sarcoma established by single cell transplantation

A new hypodiploid stemline of the long-lasting ascites sarcoma, Hirosaki sarcoma (HS), was established by means of single-cell transplantation, and its G-, C- and NOR-banding patterns were compared with those of the predecessor stemline, with special notice taken of the structural alteration of marker chromosomes. Their chromosomal relationship was well explained by the rearrangement, t(M7pM8q): Translocation of the short arm of marker M7 to the NOR of marker M8 produced a new marker M8t, and the translocation-carrying variant cells grew into a subline. A new translocation-carrying stemline was formed from this subline by single-cell transplantation. Judging from the size and number of silver-positive NORs, the NOR activity was significantly higher in this stemline than in its predecessor. The increased NOR activity might have been partly responsible for the growth of a translocation-carrying variant cell into a new subline. Single-cell-mass transplantation may be one of the most effective systems for studying the proliferative ability of subline cells and for understanding the mechanism of stemline formation in transplantable rat ascites sarcomas.

Development of silver stained structures during spermatogenesis in different genera of Formicidae

Development of silver stained structures during the spermatogenesis of Tapinoma nigerrlum, Pheidole pallidula, Tetramorium caespitum, Tetramorium semilaeve, Lasius niger and Plagiolepis schmitzii are studied. Nucleolar masses are only observed in early prophase. Obvious NORs are present in metaphase in all genera and species studied. However, there are no nucleolar Ag precipitates after metaphase. A resumption of silver stainability occurs in round spermatids. The majority of these genera present differential activity between the existing NORs. In T. nigerrimum there is primary or secondary NOR activity in all chromosomes of the complement, although there are interpopulation differences in relation to the NOR activity. In the remaining genera only certain chromosomes present NOR activity. Interpopulation genetic differences and environmental factors can cause differential activity of secondary NORs as observed in Tapinoma nigerrimum.

The direct measurement of ribosomal RNA gene activity in wheat–rye hybrids

Cloned rDNA segments, from wheat (Triticum aestivum) and rye (Secale cereale), which included the entire spacer region plus parts of the flanking 18S and 26S rRNA genes, were used to assay transcripts formed in the nuclei from wheat–rye hybrids. The tetraploid triticales (× Triticosecale Wittmack) carrying a complete rye chromosome complement and a combination of wheat chromosomes, as well as wheat and rye per se, were studied. Nuclei isolated from young leaves were incubated in the presence of [32P]UTP for 10 min, after which the total RNA was isolated. Hybridization of this radioactive RNA to the cloned rDNA segments showed that the suppression of rye NOR activity, measured cytologically, can be directly related to a major reduction in rRNA synthesis.Key words: NOR suppression, RNA transcripts, isolated nuclei.

A study of the Ag-staining significance in mitotic NOR's

The biological significance of nucleoli and mitotic Ag-staining NOR's has been the cause of controversy for several years. Whereas several authors state or assume a direct correlation between transcriptional activity and Ag-staining, others deny this hypothesis or claim a correlation between Ag-staining and decondensation of the NOR chromatin. Our results show that a decondensed state of the NOR chromatin is necessary but not sufficient to permit silver impregnation, allowing us to conclude that transcriptional NOR activity in the previous interphase is additionally required for silver staining.

Elimination of Solanum phureja nucleolar chromosomes in S. tuberosum + S. phureja somatic hybrids

The karyotype of the dihaploid SVP1 line of S. tuberosum (2n=2x=24) showed two nucleolar chromosomes with differently sized satellites. The diploid SVP5 line (2n=2x=24) and tetraploid regenerants of S. phureja had larger but similar satellites. Somatic hybrids between the diploid lines of these potato species with genome combinations 4 tub + 2 ph (plants 1-3), 2 tub + 4 ph (plants 4-7) and 4 tub + 4 ph (plant 8) had lost 2 phureja nucleolar chromosomes if 4 phureja genomes were present. One phureja nucleolar chromosome of plants 1-3 and both of plants 5 and 7 had rearranged satellites. Elimination of the two nucleolar chromosomes occurred preferentially, was under genetic control, and probably took place during early callus development. NOR activity resulting in rear-rangements between NORs may have caused the elimination.

Random acrocentric bivalent associations in human pachytene spermatocytes. Molecular implications in the occurrence of Robertsonian translocations.

Acrocentric bivalent associations were studied in 232 human male germ cells at pachytene in order to understand better the preferential involvement of chromosomes 13, 14, and 21 in Robertsonian translocations. The tendency of each acrocentric bivalent to associate with another was not correlated with NOR activity, as measured by silver staining. Good agreement was noticed between their ability to associate and the amount of satellite DNA in human acrocentric chromosomes. The distribution of two-by-two acrocentric bivalent associations was random. In order to reconcile this result with the nonrandom distribution of Robertsonian translocations, a molecular hypothesis is proposed. The model is based on homology of recombinational sites, interspersed at regular interval in satellite DNA, which could increase the probability of accidental unequal crossing-over between two specific acrocentric chromosomes.

Nucleolus organizer competition in Triticum aestivum — Aegilops umbellulata chromosome addition lines

The nucleolar organizer activity of wheat (Triticum aestivum, AABBDD) and Aegilops umbellulata (UU) chromosomes have been analyzed in the complete set of the chromosome addition lines by using a highly reproducible silver-staining procedure. Chromosomes 1U and 5U produce the partial inactivation of wheat nucleolar organizer chromosomes 6B, 1B and 5D. The chromosomes D and G from Ae. umbellulata, which are not SAT-chromosomes, seem to specifically influence the activity of wheat NORs. The predominant status of the U genome with respect to nucleolar competition in the Triticeae is confirmed.

Nucleolar organizer competition in Aegilops–rye hybrids

The nucleolar organizer activity in several Aegilops × rye hybrids (A. triuncialis × Secale cereale, A. variabilis × S. cereale, A. biunicialis × S. cereale, A. biuncialis × S. vavilovii, A. juvenalis × S. cereale) is analyzed by using a highly reproducible silver-staining procedure. The 1U and 5U chromosomes show a strong nucleolar activity, suppressing the NOR activity of chromosome 1R from rye in all the hybrid combinations (UCR, USvR, UMbR, UMbRv, and UMjDR). The nucleolus organizer chromosomes from the genomes C, Sv, Mb, and Mj show small activities. Our results confirm previous data of the nucleolar organizer activity predominant status of the 1U and 5U chromosomes from the U genome (A. umbellulata) and the weakest condition of the 1R chromosome from rye. A diagram showing the relationships between the nucleolar organizer activities of chromosomes from different genomes of Triticeae is presented.Key words: nucleolar competition, amphiplasty, Ag-NORs, Triticeae, Aegilops, Secale.

Spontaneous triploidy and NOR activity in Eigenmannia sp. (Pisces, Sternopygidae) from the Amazon basin

The occurrence of a natural triploid among diploid individuals of Eigenmannia sp from the Amazon basin is described. The diploid individuals had 2n=31 and 32 chromosomes, the difference in chromosome number being due to a Robertsonian rearrangement. The triploid individual presented 2n=46 and had two fused acrocentrics. NOR activity was present in the three homologues of triploid and a NOR polymorphism was detected in the triploid and diploids.

NOR activity, heterochromatin differentiation, and the Robertsonian polymorphism in Sus scrofa L.

The karyotype of the European wild pig (Sus scrofa scrofa L.) was analysed by means of silver-staining and the chromomycin A3/distamycin A/DAPI fluorescent banding technique to locate active NORs and to differentiate types of C-bands. The ribosomal RNA genes are localized at the secondary constrictions of chromosomes 8 and 10. All biarmed chromosomes, with the exception of chromosome 15/17 and the Y, had a chromomycin bright centromeric region that was moderately fluorescent with distamycin A/DAPI (DA/DAPI). Conversely, all acrocentric chromosomes and the Robertsonian fusion product (15/17) exhibited DA/DAPI bright centromeric heterochromatin. The results are compared with the chromosomal staining behavior of the domestic pig (Sus scrofa domestica L.) and discussed with respect to presumptive mechanisms of karyotypic evolution.

Reduced NOR association frequency in a 13/18 translocation chromosome. A family study.

The association frequency of a functional, intercalary NOR in fibroblasts of five carriers of a translocation t(13;18) was significantly lower than the average association frequency of normal G- and D-group chromosomes in the same carriers. This decreased coefficient of association does not seem to be attributable to partial loss of the NOR during rearrangement or to a loss of NOR activity, as indicated by silver staining. It is hypothesized that either (1) interphase associations including this chromosome form less frequently or, more likely, (2) associations with this chromosome are differentially susceptible to physical disruption due to flattening of association complexes during cell preparation. The presence of this abnormal NOR chromosome did not affect the association behavior of normal G- and D-group chromosomes in carrier cells. In addition, the present study supports previous observations that G-group chromosomes associate with a greater average frequency than D-group chromosomes.