Biodiversity of SSB proteins in the kingdom of bacteria

Single-strand binding proteins (SSB) are small molecules that bind to single stranded DNA to maintain its primary structure. Their C-terminal ends interact also with other proteins to activate them. These proteins assist in processes replication, recombination and repair of DNA. The C-terminal end is highly conserved. The most repeated combinations of last four amino acids are DIPF, DLPF, EIPF, ELPF. Further analysis of the last ten residues of this part of molecule, revealed that it is dominated by negatively charged and hydrophobic amino acids. Not only C-terminal end is very specific for them but also their surrounding genes. In 2003, the research group from the Netherlands presented that genes encoding SSB proteins occur very often in the neighbourhood of the genes of the ribosomal protein S6, ribosomal protein S18 and excinuclease ABC subunit A. Since 2003, the number of sequenced Bacteria increased from 69 to more than 1600 organisms. Our new study revealed that in addition to these three mentioned above genes, also the ribosomal protein L9 and major facilitator superfamily transporter occur very often.A lot of bacteria have more than one gene encoding SSB protein. In most cases, these additional ssb genes have completely different composition of the C-terminal ends and also different surrounding genes. The evidence confirming their SSB function, is the existence of distinctive oligonucleotide/oligosaccharide-binding (OB) domain, also known as OB fold, which bind to DNA to protect it against forming of the secondary structures.status: publishe