In 1996, a trinucleotide circular code X is identified in genes of prokaryotes and eukaryotes (Arquès and Michel, 1996). In 2012, X motifs are identified in the transfer RNA (tRNA) Phe and 16S ribosomal RNA (Michel, 2012). A statistical analysis of X motifs in all available tRNAs of prokaryotes and eukaryotes in the genomic tRNA database (September 2012, http://lowelab.ucsc.edu/GtRNAdb/, Lowe a...

The presence of shared conserved insertion or deletions (indels) in protein sequences is a special type of signature sequence that shows considerable promise for phylogenetic inference. An alternative model of microbial evolution based on the use of indels of conserved proteins and the morphological features of prokaryotic organisms is proposed. In this model, extant archaebacteria and gram-pos...