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  • 1
    Electronic Resource
    Electronic Resource
    Unmethylated regions in the intergenic spacer of maize and teosinte ribosomal RNA genes (1990)
    Springer
    Plant molecular biology 14 (1990), S. 333-347 
    Details
    ISSN: 1573-5028
    Keywords: intergenic spacer ; maize ; methylation ; rDNA ; teosinte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The restriction endonucleases Hpa II and Msp I were used to examine cytosine methylation in the ribosomal RNA genes (rDNA) of inbred lines of maize and species of teosinte. In all of the rDNAs examined, Msp I (not sensitive to mCpG) digestion yielded a distribution of lower molecular weight fragments indicative of multiple recognition sites. The majority of the rDNA arrays in an individual were inaccessible to Hpa II (sensitive to mCpG) cleavage, but a significant fraction (10–25%) was cleaved at least once by Hpa II into repeat unit length fragments (9.1 kbp). In some maize inbred lines, one or two additional fragment populations (less than 9.1 kbp in length) were also produced by Hpa II digestion. All of the unmethylated Hpa II sites mapped to the intergenic spacer (IGS), and the major unmethylated site was located approximately 800 bp 5′ to the start of the 18S RNA coding sequence. An Eco RI polymorphism, present in the 26S gene of certain inbred lines and hybrids, was utilized to investigate the organization of unmethylated repeat units in the rDNA array. In double digest experiments with Hpa II/Eco RI, the fragments from repeat units with two Eco RI sites were sensitive to Hpa II digestion, whereas, the fragments from repeat units with a single Eco RI site were almost completely resistant to Hpa II digestion. Similar digestion patterns were also observed in Eco RII (sensitive to mCNG)/Eco RI digests. These results suggest that unmethylated and Eco RI polymorphic sites occur in the same repeat units.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00028770
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  • 2
    Electronic Resource
    Electronic Resource
    DNaseI-sensitive and undermethylated rDNA is preferentially expressed in a maize hybrid (1993)
    Springer
    Plant molecular biology 21 (1993), S. 805-821 
    Details
    ISSN: 1573-5028
    Keywords: DNaseI sensitivity ; maize ; methylation ; nucleolar dominance ; rDNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An Eco RI polymorphism, present in the 26S ribosomal RNA gene (rDNA) of the maize hybrid Sx19 (B73×Mo17), was utilized to correlate DNaseI sensitivity, undermethylation and expression in rDNA. We had previously shown that in double digest experiments with methylation-sensitive restriction enzymes and Eco RI, Sx19 rDNA fragments originating from repeat units with two Eco RI sites (8.0 kb) are undermethylated, whereas the fragments originating from repeat units with a single Eco RI site (9.1 kb) are completely methylated. In the present study, Sx19 rDNA chromatin structure was examined by purifying intact nuclei and digesting them briefly with increasing amounts of DNaseI. Analysis of this DNA with Eco RI showed that the 8.0 kb rDNA fragments are extremely sensitive to DNaseI digestion, while the 9.1 kb rDNA fragments are relatively resistant to digestion even at high levels of DNasel. Specific sites hypersensitive to DNaseI cleavage were mapped to a region in the intergenic spacer (IGS) near the major undermethylated site. Analysis of polymerase chain reaction (PCR) products synthesized using Sx19, B73, and Mo17 DNAs as templates indicated that the Eco RI polymorphism is due to a base change in the recognition site. Direct rRNA sequencing identified a single-base change in Mo17 rRNA relative to B73 rRNA. Allele-specific oligonucleotide probes containing the region surrounding and including the Eco RI polymorphic site were utilized to detect a nucleolar dominance effect by quantitating levels of rRNA transcripts in Sx19 and the reciprocal cross. Results from these single-base-pair mismatch hybridization experiments indicate that the majority of the rRNA transcripts in Sx19 orginate from the DNaseI-sensitive, undermethylated, Eco RI-polymorphic rDNA repeat units.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00027113
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  • 3
    Electronic Resource
    Electronic Resource
    Ribosomal RNA sequences for inferring phylogeny within the grass family (Poaceae) (1988)
    Springer
    Plant systematics and evolution 160 (1988), S. 29-37 
    Details
    ISSN: 1615-6110
    Keywords: Angiosperms ; Poaceae ; Evolution ; phylogenetic trees ; 18 S rRNA ; 26 S rRNA ; direct rRNA sequencing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have isolated RNA from nine different grass species and fromPsilotum, a modern representative of a primitive land plant lineage. By direct RNA sequencing with reverse transcriptase, we have determined the nucleotide sequence for five regions of the 18 S rRNA molecule and three regions of the 26 S rRNA molecule. Over 1 600 positions have been elucidated for each plant species. These sequences were aligned by computer and the variable positions were identified by inspection. The data from the variable positions were input into phylogenetic inference computer programs to generate an evolutionary relationship among the grass species. This evolutionary tree based on nucleotide sequence data was compared to a recent classification of thePoaceae based on morphological data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00936707
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