How small are small mutation rates?

We consider evolutionary game dynamics in a finite population of size N. When mutations are rare, the population is monomorphic most of the time. Occasionally a mutation arises. It can either reach fixation or go extinct. The evolutionary dynamics of the process under small mutation rates can be approximated by an embedded Markov chain on the pure states. Here we analyze how small the mutation rate should be to make the embedded Markov chain a good approximation by calculating the difference between the real stationary distribution and the approximated one. While for a coexistence game, where the best reply to any strategy is the opposite strategy, it is necessary that the mutation rate μ is less than N ^−1/2exp[−N] to ensure that the approximation is good, for all other games, it is sufficient if the mutation rate is smaller than (N ln N)⁻¹. Our results also hold for a wide class of imitation processes under arbitrary selection intensity.     

植物小分子RNA研究进展

植物体内存在多种不同类型的小分子RNA(small RNA,sRNA),在调节植物生长发育、抑制转座子活性和抵御逆境等过程中发挥着重要的作用。近年来,人们在sRNA的产生机制、效应复合物的形成和对靶基因的调控方式及其生物学功能等方面的研究取得了很大进展。该文对这些进展作简要介绍。     

Regulatory small RNAs

Recent years have been marked by a burst of studies on the role of various RNAs in the regulation of gene expression. These regulatory effects act on the level of both chromatin in the nuclei and the cytoplasm during translation. The review papers of this issue are mainly dedicated to different types of small RNAs of 20–30 nucleotides. The small RNAs control diverse cellular functions including genome protection against transpositions of mobile elements of the genome.     

Intercomparison of small biomolecules by gel filtration and small angle scattering

This paper describes how small angle neutron scattering (SANS) can be used to confirm that gel filtration results are free of dimerization effects. After characterization by analytical gel filtration, concentrated solutions (in heavy water, D2O) of a cobra neurotoxin, a cytotoxin, and a cytotoxin analog are studied by SANS. Small differences in shape are shown to be discernible by means of least-square fits to ellipsoidal models. The parallel axis theorem is then invoked to assess dimerization levels statistically. The results are briefly discussed on the basis of function in relation to structure.     

A small pressure chamber for use with plant leaves of small size

Summary A pressure chamber for use with small leaves can be constructed out of commercially available parts. re]19770203     

Non-coding RNAs: lessons from the small nuclear and small nucleolar RNAs

Recent advances have fuelled rapid growth in our appreciation of the tremendous number, diversity and biological importance of non-coding (nc)RNAs. Because ncRNAs typically function as ribonucleoprotein (RNP) complexes and not as naked RNAs, understanding their biogenesis is crucial to comprehending their regulation and function. The small nuclear and small nucleolar RNPs are two well studied classes of ncRNPs with elaborate assembly and trafficking pathways that provide paradigms for understanding the biogenesis of other ncRNPs.     

核仁小RNA源性小RNA

最新研究结果表明,一些与RNA介导基因沉默相关的小RNA由核仁小RNA(small nucleolar RNA,snoRNA)加工产生,这种小RNA被称为核仁小RNA源性小RNA(snoRNA derived small RNA,sdRNA)。sdRNA现象分布物种广;涉及的snoRNA种类全,数量多;产生的小RNA分子大小不一、数量、种类多。表明这种小RNA在生物中存在着广泛的普遍性。sdRNA的发现拓展了snoRNA的功能,揭示了snoRNA与RNA介导的基因沉默之间的紧密关系,增强了snoRNA在RNA调控网络中的重要性,并为进一步研究RNA调控网络开启了一扇门。