Comparative analysis of amino acid sequences in particular domains of Hoc proteins in Teequatrovirinae subfamily bacteriophages

The work presents the results of comparative research into immunoglobulinlike domains in the genomes of T4-related bacteriophages. Hoc proteins are proposed to be used for classification of the Teequatrovirinae phage subfamily. Particular domains in 31 Hoc proteins of the subfamily were subjected to phylogenetic analysis. The number of domains in Hoc proteins of different bacteriophages in the subfamily was shown to vary from one to five. Based on this, bacteriophages can be divided into six subgroups. The phylogenetic tree of the domains in hoc gene product proteins of T4-related bacteriophages forms three major branches. These are the branches of C-terminal, Nterminal and intermediate domains. The obligatory occurrence of the C-terminal domain in all Hoc proteins is indicative of its functional and structural significance for the formation of the protein and its attachment to phage’s capsid. Hypothetical schemes for the evolutionary origin of repeated amino acid sequences in Hoc proteins were formulated.