Functional characterization and COG assignment

Functional characterization of all the cyanobacterial genomes was done using the Clusters of Orthologous Groups (COG) database (Tatusov et al. 2003). For each of the genome, all the genes were subjected to COG assignment using Function Profile tool from IMG database (Markowitz et al. 2012). Function Profile tool assists in identification of the genes associated with a particular function in query genome and thus, genes are expected to share at least the same general functions with their COG matches. Once the genes were assigned COGs, they were clustered in 22 functional categories, which were further grouped in four major classes (Table 2). Self-made Perl scripts were used for the grouping of different COG categories.

Functional distribution of cyanobacterial genomes under consideration (values represents percentage of the particular COG category identified in the cyanobacteria)

COG categories: E amino acid transport and metabolism, G carbohydrate transport and metabolism, F nucleotide transport and metabolism, C energy production and conversion, H coenzyme transport and metabolism, I lipid transport and metabolism, P inorganic ion transport and metabolism, Q secondary metabolites biosynthesis, transport and catabolism, D cell cycle control, cell division, chromosome partitioning, M cell wall/membrane/envelope biogenesis, N cell motility, O posttranslational modification, protein turnover, chaperones, T signal transduction mechanisms, U intracellular trafficking, secretion, and vesicular transport, V defense mechanisms, A RNA processing and modification, B chromatin structure and dynamics, J translation, ribosomal structure and biogenesis, K Transcription, L replication, recombination and repair, S function unknown, R general function prediction only