SsbB

SsbB is a single-stranded DNA-binding protein found in certain Gram-positive bacteria, most notably Bacillus subtilis and closely related species. It is part of the competence-induced protein set and is distinguished from the housekeeping SsbA that functions in general DNA replication and repair.

Role and function

SsbB is produced during natural competence, the process by which bacteria take up exogenous DNA from the environment. It binds the internalized single-stranded DNA (ssDNA) that enters the cell, protecting it from nucleases and preventing the formation of deleterious secondary structures. By stabilizing the incoming ssDNA, SsbB aids in the processing and, ultimately, the recombination of transforming DNA with the recipient chromosome. It is not essential for viability but increases transformation efficiency.

Regulation and expression

Expression of ssbB is regulated by the competence regulatory network, including the master regulator ComK. The ssbB gene is typically co-regulated with other competence genes and is induced when cells commit to genetic transformation.

Structure and interactions

SsbB binds ssDNA with high affinity and forms nucleoprotein complexes appropriate for transient, uptake-related substrates rather than chromosomal replication. In competence, SsbB operates in concert with other factors, notably DprA and RecA. DprA facilitates RecA loading onto the bound ssDNA, promoting homologous recombination and integration of transforming DNA.

Distribution and significance

SsbB homologs are primarily found in Bacillales and related taxa. While SsbA remains essential for replication and general DNA metabolism, SsbB provides a specialized function that enhances the efficiency of horizontal gene transfer through natural competence. Understanding SsbB contributes to insights into bacterial DNA uptake and genetic exchange.

See also

SsbA, natural competence, DprA, RecA.