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131.
132.
Replication slippage may cause parallel evolution in the secondary structures of mitochondrial transfer RNAs 总被引:9,自引:4,他引:5
Presence of the dihydrouridine (D) stem in the mitochondrial cysteine tRNA
is unusually variable among lepidosaurian reptiles. Phylogenetic and
comparative analyses of cysteine tRNA gene sequences identify eight
parallel losses of the D-stem, resulting in D-arm replacement loops.
Sampling within the monophyletic Acrodonta provides no evidence for
reversal. Slipped-strand mispairing of noncontiguous repeated sequences
during replication or direct replication slippage can explain repeats
observed within cysteine tRNAs that contain a D-arm replacement loop. These
two mechanisms involving replication slippage can account for the loss of
the cysteine tRNA D-stem in several lepidosaurian lineages, and may
represent general mechanisms by which the secondary structures of
mitochondrial tRNAs are altered.
相似文献
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J. M. McGrath C. A. Derrico Y. Yu 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1999,98(6-7):968-976
Diversity among sugar beet accessions released over the first 50 years of public breeding in the United States was examined
to ascertain a baseline of genetic diversity and to gauge the effect of breeding on the loss or gain of diversity over this
time period. Accessions were chosen as released germplasm from the major breeding stations contributing to the US germplasm
pool and their presumed ancestors from Europe, including representatives for the wild forms Beta vulgaris ssp. maritima. Sixty nine polymorphic RAPD fragments were used for gene frequency analysis, and heterozygosity was determined within and
among groups of accessions related either by breeding station or simply inherited agronomic characters for monogerm seed and
restoration of fertility in a cytoplasmic male-sterile background. In general, heterozygosity within releases declined with
time, but total genetic diversity in the US germplasm pool remained constant. Breeding for the agronomic characters had a
marked influence in reducing diversity.
Received: 20 October 1998 / Accepted: 28 October 1998 相似文献
137.
T A Kavanagh N D Thanh N T Lao N McGrath S O Peter E M Horváth P J Dix P Medgyesy 《Genetics》1999,152(3):1111-1122
Efficient plastid transformation has been achieved in Nicotiana tabacum using cloned plastid DNA of Solanum nigrum carrying mutations conferring spectinomycin and streptomycin resistance. The use of the incompletely homologous (homeologous) Solanum plastid DNA as donor resulted in a Nicotiana plastid transformation frequency comparable with that of other experiments where completely homologous plastid DNA was introduced. Physical mapping and nucleotide sequence analysis of the targeted plastid DNA region in the transformants demonstrated efficient site-specific integration of the 7.8-kb Solanum plastid DNA and the exclusion of the vector DNA. The integration of the cloned Solanum plastid DNA into the Nicotiana plastid genome involved multiple recombination events as revealed by the presence of discontinuous tracts of Solanum-specific sequences that were interspersed between Nicotiana-specific markers. Marked position effects resulted in very frequent cointegration of the nonselected peripheral donor markers located adjacent to the vector DNA. Data presented here on the efficiency and features of homeologous plastid DNA recombination are consistent with the existence of an active RecA-mediated, but a diminished mismatch, recombination/repair system in higher-plant plastids. 相似文献
138.
Transplastomic tobacco plants expressing a fatty acid desaturase gene exhibit altered fatty acid profiles and improved cold tolerance 总被引:4,自引:0,他引:4
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Epidermal growth factor receptor (EGFR) plays a critical role in the promotion of epithelial cell proliferation and migration. Previous studies have suggested a cooperative role between EGFR and integrin signalling pathways that enable efficient adhesion and migration but the mechanisms controlling this remain poorly defined. Here, we show that EGFR forms a complex with focal adhesion kinase in epithelial cells. Surprisingly, this complex enhances local Src activity at focal adhesions to promote phosphorylation of the cytoskeletal adaptor protein ezrin at Y478, leading to actomyosin contractility, suppression of focal adhesion dynamics and slower migration. We further demonstrate this regulation of Src is due to the suppression of PTP1B activity. Our data provide new insight into EGF-independent cooperation between EGFR and integrins and suggest transient interactions between these kinases at the leading edge of cells act to spatially control signalling to permit efficient motility. 相似文献