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991.
992.
We isolated RNAs by selection–amplification, selecting for affinity to Phe–Sepharose and elution with free l-phenylalanine. Constant sequences did not contain Phe condons or anticodons, to avoid any possible confounding influence
on initially randomized sequences. We examined the eight most frequent Phe-binding RNAs for inclusion of coding triplets.
Binding sites were defined by nucleotide conservation, protection, and interference data. Together these RNAs comprise 70%
of the 105 sequenced RNAs. The K
D for the strongest sites is ≈50 μM free amino acid, with strong stereoselectivity. One site strongly distinguishes free Phe from Trp and Tyr, a specificity
not observed previously. In these eight Phe-binding RNAs, Phe codons are not significantly associated with Phe binding sites.
However, among 21 characterized RNAs binding Phe, Tyr, Arg, and Ile, containing 1342 total nucleotides, codons are 2.7-fold
more frequent within binding sites than in surrounding sequences in the same molecules. If triplets were not specifically related to binding sites, the probability of this distribution would be 4.8 × 10−11. Therefore, triplet concentration within amino acid binding sites taken together is highly likely. In binding sites for Arg,
Tyr, and Ile cognate codons are overrepresented. Thus Arg, Tyr, and Ile may be amino acids whose codons were assigned during
an era of direct RNA–amino acid affinity. In contrast, Phe codons arguably were assigned by another criterion, perhaps during
later code evolution. 相似文献
993.
994.
Caetano-Anollés G 《Journal of molecular evolution》2002,54(3):333-345
The origin and diversification of RNA secondary structure were traced using cladistic methods. Structural components were
coded as polarized and ordered multi-state characters, following a model of character state transformation outlined by considerations
in statistical mechanics. Several classes of functional RNA were analyzed, including ribosomal RNA (rRNA). Considerable phylogenetic
signal was present in their secondary structure. The intrinsically rooted phylogenies reconstructed from evolved RNA structure
depicted those derived from nucleic acid sequence at all taxonomical levels, and grouped organisms in concordance with traditional
classification, especially in the archaeal and eukaryal domains. Natural selection appears therefore to operate early in the
information flow that originates in sequence and ends in an adapted phenotype. When examining the hierarchical classification
of the living world, phylogenetic analysis of secondary structure of the small and large rRNA subunits reconstructed a universal
tree of life that branched in three monophyletic groups corresponding to Eucarya, Archaea, and Bacteria, and was rooted in
the eukaryotic branch. Ribosomal characters involved in the translational cycle could be easily traced and showed that transfer
RNA (tRNA) binding domains in the large rRNA subunit evolved concurrently with the rest of the rRNA molecule. Results suggest
it is equally parsimonious to consider that ancestral unicellular eukaryotes or prokaryotes gave rise to all extant life forms
and provide a rare insight into the early evolution of nucleic acid and protein biosynthesis.
Received: 13 September 2000 / Accepted: 27 August 2001 相似文献
995.
996.
997.
998.
Noveroske JK Lai L Gaussin V Northrop JL Nakamura H Hirschi KK Justice MJ 《Genesis (New York, N.Y. : 2000)》2002,32(3):218-230
For nearly 40 years functional studies of the mouse quaking gene (qkI) have focused on its role in the postnatal central nervous system during myelination. However, the homozygous lethality of a number of ENU-induced alleles reveals that quaking has a critical role in embryonic development prior to the start of myelination. In this article, we show that quaking has a previously unsuspected and essential role in blood vessel development. Interestingly, we found that quaking, a nonsecreted protein, is expressed in the yolk sac endoderm, adjacent to the mesodermal site of developing blood islands, where the differentiation of blood and endothelial cells first occurs. Antibodies against PE-CAM-1, TIE-2 and SM-alpha-actin reveal that embryos homozygous for the qk(k2) allele have defective yolk sac vascular remodeling and abnormal vessels in the embryo proper at midgestation, coinciding with the timing of embryonic death. However, these mutants exhibit normal expression of Nkx2.5 and alpha-sarcomeric actin, indicating that cardiac muscle differentiation was normal. Further, they had normal embryonic heart rates in culture, suggesting that cardiac function was not compromised at this stage of embryonic development. Together, these results suggest that quaking plays an essential role in vascular development and that the blood vessel defects are the cause of embryonic death. 相似文献
999.
In a screen of nuclear genes that assist splicing of mitochondrial localized group II introns in yeast we isolated low-copy number suppressors of splicing and respiratory-deficient point mutants of intron aI5gamma, the last intron of the gene encoding cytochrome c oxidase subunit I. One of the genes found contains the open reading frame (ORF) YGL064c that has previously been proposed to encode a putative RNA helicase of the DEAD box family. Deletion of the ORF gives rise to 100% cytoplasmic petites, indicating that the protein plays an essential role in the mitochondrial RNA metabolism. Overexpression of YGL064c-GFP fusions clearly revealed a mitochondrial localization of the protein. The gene encodes the fourth putative RNA helicase of Saccharomyces cerevisiae implicated in a mitochondrial function and was therefore termed MRH4 (for mitochondrial RNA helicase). 相似文献
1000.
Siddiqui SS 《Traffic (Copenhagen, Denmark)》2002,3(1):20-28
In eukaryotic cells members of the kinesin family mediate intracellular transport by carrying cellular cargo on microtubule tracks. The nematode Caenorhabditis elegans genome encodes 21 members of the kinesin family, which show significant homology to their mammalian orthologs. Based on motor domain sequence homology and placement of the motor domain in the protein, the C. elegans kinesins have been placed in eight distinct groups; members of which participate in embryonic development, protein transport, synaptic membrane vesicles movement and in the axonal growth. Among 21 kinesins, at least 11 play a central role in spindle movement and chromosomal segregation. Understanding the function of C. elegans kinesins and related proteins may help navigate through the intricacies of intracellular traffic in a simple animal. 相似文献