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Research pertaining to SARS-CoV-2 is in full swing to understand the origin and evolution of this deadly virus that can lead to its rapid detection. To achieve this, atypical genomic sequences which may be unique to SARS-CoV-2 or Coronaviridae family in general may be investigated. Such sequences in virus genomes may be responsible for target prediction, replication, defence mechanisms and viral packaging. This fact has motivated us to explore the different types of repeats such as palindromes, mirror repeats and inverted repeats in SARS-CoV-2, MERS-CoV and SARS-CoV-1. For this purpose, the respective reference sequence of SARS-CoV-2, MERS-CoV and SARS-CoV-1 is divided into descriptors of sequences of length ${k}$ using ${k}$ -mer technique. Thereafter, these descriptors are represented as a collection of tokens which are subsequently used for the identification of palindrome, mirror repeat and inverted repeat in the respective reference sequence. The highest number of palindromes, mirror repeats and inverted repeats are identified for descriptor length 10. As a result, for palindromes such values are 38, 42 and 33 and for mirror repeats they are 52, 38 and 33 for SARS-CoV-2, MERS-CoV and SARS-CoV-1 respectively. For inverted repeats, with a descriptor length 10 and intervening length 5, the values are 59, 56 and 70 respectively. Moreover, the identified repeats are then searched for in 108246, 291 and 340 SARS-CoV-2, MERS-CoV and SARS-CoV-1 virus sequences respectively to find the population coverage of such repeats. It surpasses 99% in most cases and even 100% for some. Furthermore, GC contents which mostly lie between 20%-50% are evaluated for these repeats as well in order to understand their binding efficacy.

Background: The repeating elements in the genes or genomes of living organisms are associated with a variety of functions at the molecular level. Mirror repeats (MRs) are unique type of repeat sequences among them, which are found to be linked with H-DNA formation and they have also associated with several neurological disorders with many other functional roles are also being reported. Methods: The manual bioinformatics-based approach is used to identify the MRs in the genome. The applied approach FASTA-parallel complement-BLAST is used by following some simple steps to identify MRs. This methodology is initiated by the downloading of a sequence of interest in FASTA format followed by development of the parallel complement and final step of BLAST analysis. By using this approach, the present study identifies MRs in lac, trp, and ara operon genes of Escherichia coli str. K-12 substr. MG1655 (NC_000913.3). Results: Present investigation identified the frequent distribution MRs in all the analyzed operon genes. These identified MRs vary in their length or size. In case of lac, trp, and ara operon, maximum number of MRs reported in lacZ (61), trpE (40), and araE (41) genes, respectively. Conclusion: The frequent existence of MRs (shorter as well as larger length) in analyzed genes gives a hint about their significant roles in the genes or genomes of all bacterial species. These may be useful to study the evolutionary history of living world. These types of studies will be exploring new trends and tools of molecular biology research as well as development of new concept for MR identification.

Background: The repeating elements in the genes or genomes of living organisms are associated with a variety of functions at the molecular level. Mirror repeats (MRs) are unique type of repeat sequences among them, which are found to be linked with H-DNA formation and they have also associated with several neurological disorders with many other functional roles are also being reported. Methods: The manual bioinformatics-based approach is used to identify the MRs in the genome. The applied approach FASTA-parallel complement-BLAST is used by following some simple steps to identify MRs. This methodology is initiated by the downloading of a sequence of interest in FASTA format followed by development of the parallel complement and final step of BLAST analysis. By using this approach, the present study identifies MRs in lac, trp, and ara operon genes of Escherichia coli str. K-12 substr. MG1655 (NC_000913.3). Results: Present investigation identified the frequent distribution MRs in all the analyzed operon genes. These identified MRs vary in their length or size. In case of lac, trp, and ara operon, maximum number of MRs reported in lacZ (61), trpE (40), and araE (41) genes, respectively. Conclusion: The frequent existence of MRs (shorter as well as larger length) in analyzed genes gives a hint about their significant roles in the genes or genomes of all bacterial species. These may be useful to study the evolutionary history of living world. These types of studies will be exploring new trends and tools of molecular biology research as well as development of new concept for MR identification. [ABSTRACT FROM AUTHOR]

Inverted duplicates are a type of repetitive DNA motifs consist of two copies of reverse complementary sequences separated by a spacer sequence. They can lead to genome instability and manymay have no function, but some functional small RNAs are processed from hairpins transcribed from these elements. It is not clear whether the pervasivenumbers of such elements in genomes, especially those of mammals, is the result of high generation rates of neutral or slightly deleterious duplication events or positive selection for functionality. To test the functionality of intergenic inverted duplicates without knownfunctions, we used mirror duplicates, a type of repetitive DNAmotifs with few reported functions and little potential to form hairpins when transcribed, as a nonfunctional control. We identified large numbers of inverted duplicates within intergenic regions of human and mouse genomes, as well as 19 other vertebrate genomes. Structure characterization of these inverted duplicates revealed higher proportion to form stable hairpins compared with converted mirror duplicates, suggesting that inverted duplicates may produce hairpin RNAs. Expression profiling across tissues demonstrated that 7.8% of human and 5.7%ofmouse inverted duplicates were expressed even under strict criteria. Wefound that expressed inverted duplicates were more likely to be structurally stable than both unexpressed inverted duplicates and expressed converted mirror duplicates. By dating inverted duplicates in the vertebrate phylogenetic tree, we observed higher conservation of inverted duplicates thanmirror duplicates. These observations support the notion that expressed inverted duplicatesmay be functional through forming hairpin RNAs. [ABSTRACT FROM AUTHOR]

Abstract: RepeatAround is a Windows based software tool designed to find “direct repeats”, “inverted repeats”, “mirror repeats” and “complementary repeats”, from 3 to 64bp length, in circular genomes. It processes input files directly extracted from GenBank database, providing visualisation of the repeats location in the genomic structure, so that for instance, in most mtDNAs the user can check if the repeats are located in coding or non-coding region (and in the first case in which gene), and how far apart the repeat pair(s) are. Besides the visual tool, it provides other outputs in a spreadsheet containing information on the number and location of the repeats, facilitating graphic analyses. Several genomes can be inputed simultaneously, for phylogenetic comparison purposes. Other capabilities of the software are the generation of random circular genomes, for statistical evaluation of comparison between observed repeats distributions with their shuffled counterparts, as well as the search for specific motifs, allowing an easy confirmation of repeats flanking a newly detected rearrangement. As an example of the programme’s applications we analysed the Direct Repeats distribution in a large human mtDNA database. Results showed that Direct Repeats, even the larger ones, are evenly distributed among the human mtDNA haplogroups, enabling us to state that, based only on the repetitive motifs, no haplogroup is particularly more or less prone to mtDNA macrodeletions. [Copyright &y& Elsevier]