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Reiterated transfer RNA genes of Xenopus laevis
- Source :
- Journal of Molecular Biology. 79:391-410
- Publication Year :
- 1973
- Publisher :
- Elsevier BV, 1973.
-
Abstract
- The proportion of the Xenopus laevis genome complementary to ā7 Sā RNA, unfractionated transfer RNA and some selected aminoacyl-tRNAs, and the sequence complexity of these RNA species, have been determined by following the kinetics of RNA-DNA hybridization on filters under conditions of RNA excess at optimum rate temperature. For hybridization of aminoacyl-labelled tRNAs, conditions for optimum aminoacylation were first determined and, where necessary, aminoacyl-tRNAs were treated with nitrous acid to prevent discharge during annealing. Neither the extent nor rate of hybridization was affected by this treatment. ā7 Sā RNA, coded for by 580 genes per haploid complement of chromosomes, reacts like a single family of nucleotide sequences, whereas about 43 basic tRNA sequences are coded for by at least 7800 genes. If hybrids are not treated with RNase A, the apparent tDNA redundancy is some 23% greater but no more nucleotide sequences are detectable. Taken together, the results suggest that each tRNA sequence is, on average, 200-fold reiterated. The reiteration varies, however, for different aminoacyl-tRNAs. Thus, hybridization resolves only one valyl-tRNA which is coded for by 240 genes, but at least four leucyl-tRNA sequences can be distinguished by hybridization, each of which is on average 90-fold reiterated. Reiteration also varies for the two methionyl-tRNAs detectable both by hybridization and by reversed phase chromatography: tRNA1Met and tRNA2Met are 310- and 170-fold reiterated, respectively, and each is kinetically homogeneous. These saturation values are almost exactly additive and are not influenced by the presence of other tRNA species. Thus the results suggest that Xenopus tRNAs are no more heterogeneous than would be predicted by the genetic code, despite the high but variable multiplicity of tRNA cistrons.
- Subjects :
- Transfer DNA
RNase P
Xenopus
Aminoacylation
Haploidy
Kidney
Sulfur Radioisotopes
Tritium
Chromatography, DEAE-Cellulose
Amino Acyl-tRNA Synthetases
Methionine
Ribonucleases
RNA, Transfer
Structural Biology
Centrifugation, Density Gradient
Animals
Carbon Radioisotopes
Molecular Biology
Gene
Cells, Cultured
Nitrites
Genetics
Base Sequence
biology
Temperature
Nucleic Acid Hybridization
RNA
Chromatography, Ion Exchange
Genetic code
biology.organism_classification
Kinetics
Genes
Liver
Transfer RNA
Chromatography, Gel
Spectrophotometry, Ultraviolet
Subjects
Details
- ISSN :
- 00222836
- Volume :
- 79
- Database :
- OpenAIRE
- Journal :
- Journal of Molecular Biology
- Accession number :
- edsair.doi.dedup.....01d886ec10af07ae2f6f83c27497d61f