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1.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
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Identification of the signalling molecules involved in mesoderm formation in amphibian embryos still presents problems. None of the original candidates, such as activin, have been definitively ruled out, and the new factors, such as the nodal-related genes, have come on to the scene. Of the original candidates, activin has been definitively shown to act as a morphogen, whereas bone morphogenetic protein (BMP)-4 has emerged as a ventral inducer and an inhibitor of neural differentiation. The effects of BMP-4 are antagonized by chordin, a molecule related to the product of the Drosophila gene short gastrulation. 相似文献
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Ants are powerful model systems for the study of cooperation and sociality. In this review, we discuss how recent advances in ant genomics have contributed to our understanding of the evolution and organization of insect societies at the molecular level. 相似文献
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Single-Molecule Force Spectroscopy Study on the Mechanism of RNA Disassembly in Tobacco Mosaic Virus
Ningning Liu Ying Chen Bo Peng Yuan Lin Qian Wang Zhaohui Su Wenke Zhang Hongbin Li Jiacong Shen 《Biophysical journal》2013,105(12):2790-2800
To explore the disassembly mechanism of tobacco mosaic virus (TMV), a model system for virus study, during infection, we have used single-molecule force spectroscopy to mimic and follow the process of RNA disassembly from the protein coat of TMV by the replisome (molecular motor) in vivo, under different pH and Ca2+ concentrations. Dynamic force spectroscopy revealed the unbinding free-energy landscapes as that at pH 4.7 the disassembly process is dominated by one free-energy barrier, whereas at pH 7.0 the process is dominated by one barrier and that there exists a second barrier. The additional free-energy barrier at longer distance has been attributed to the hindrance of disordered loops within the inner channel of TMV, and the biological function of those protein loops was discussed. The combination of pH increase and Ca2+ concentration drop could weaken RNA-protein interactions so much that the molecular motor replisome would be able to pull and disassemble the rest of the genetic RNA from the protein coat in vivo. All these facts provide supporting evidence at the single-molecule level, to our knowledge for the first time, for the cotranslational disassembly mechanism during TMV infection under physiological conditions. 相似文献
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The Tat (twin-arginine translocation) system from Escherichia coli transports folded proteins with N-terminal twin-arginine signal peptides across the cytoplasmic membrane. The influence of general chaperones on Tat substrate targeting has not been clarified so far. Here we show that the chaperones SlyD and DnaK bind to a broad range of different Tat signal sequences in vitro and in vivo. Initially, SlyD and GroEL were purified from DnaK-deficient extracts by their affinity to various Tat signal sequences. Of these, only SlyD bound Tat signal sequences also in the presence of DnaK. SlyD and DnaK also co-purified with Tat substrate precursors, demonstrating the binding to Tat signal sequences in vivo. Deletion of dnaK completely abolished Tat-dependent translocation of CueO, but not of DmsA, YcdB, or HiPIP, indicating that DnaK has an essential role specifically for CueO. DnaK was not required for stability of the CueO precursor and thus served in some essential step after folding. A CueO signal sequence fusion to HiPIP was Tat-dependently transported without the need of DnaK, indicating that the mature domain of CueO is responsible for the DnaK dependence. The overall results suggest that SlyD and DnaK are in the set of chaperones that can serve as general Tat signal-binding proteins. DnaK has additional functions that are indispensable for the targeting of CueO. 相似文献
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