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Jodhpur, India

Trivedi S.,Vyas University | Hancock J.M.,University of Cambridge
Gene | Year: 2012

The locations of microsatellites in mammalian genomes are restricted by purifying selection in a number of ways. For example, with the exception of some trinucleotide repeats they are excluded from protein coding regions of genomes because of their tendency to cause frameshift mutations. Here we investigate whether purifying selection might affect the types and frequencies of microsatellites in microRNA (miRNA). We concentrate on miRNAs expressed in neurons and the brain (NB-miRNAs) as microsatellites in these genes might give rise to similar effects as disease-causing repeats in protein coding genes. We show that in human miRNAs in general AG and AT microsatellites are reduced in frequency compared to AC repeats and that NB-miRNA genes contain significantly fewer microsatellites than expected from frequencies of microsatellites in other miRNA genes. NB-miRNAs show lower levels of sequence divergence in comparisons of human-macaque orthologues and more often have detectable orthologues in non-human mammals than non-NB-miRNAs. This suggests that microsatellites in miRNAs may indeed be constrained by purifying selection and that the strength of this selection may differ between NB-miRNAs and non-NB-miRNAs. We identify a number of ways in which the potential disruption of pre-miRNA secondary structure might result in purifying selection. However other, non-selective forces could also play a role in generating the biases observed in miRNA microsatellites. © 2012 Elsevier B.V. Source


Microsatellites or simple sequence repeats (SSRs) are ubiquitous in genomes studied so far. SSR mutations or microsatellite instability (MSI) can result in either expansion or contraction of repeat units. These alterations can lead to disorders like cancer and neurodegeneration. As gleaned from studies, it appears that SSR mutations are dependent on motif size, nucleotide content and SSR length. Besides these, position of SSRs in genome (coding or non-coding sequences), presence on leading or lagging strand and distance from origin of replication also affect SSR mutations. Further, fidelity of replication and repair machinery as well as epigenetic factors may influence repeat stability. This review summarizes some of these aspects of SSR mutations that occur especially during DNA replication/repair besides epigenetic factors that influence SSR contraction or expansion. Source


Trivedi S.,Vyas University | Choudhary O.P.,Vyas University | Gharu J.,Vyas University
Recent Patents on DNA and Gene Sequences | Year: 2011

Bacteriorhodopsin (BR) is an integral membrane protein found in "purple" membrane (the Archaea cell membrane) mainly in Halobacteria. This protein absorbs green light (wavelength 500-650 nm, with the absorption maximum at 568 nm) and converts it into an electrochemical gradient. This gradient in turn is used for ATP production. The ability of BR to convert light energy into chemical energy or sunlight into electricity has been used in different applications mainly optical appliances but also for therapeutic/medical applications and research. This review surveys some of these applications that have been patented in the last five years. © 2011 Bentham Science Publishers Ltd. Source

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