The gene, coding for single-stranded-DNA-binding protein (SSB), was cloned from four marine strains that differed in their temperature and pressure optima and ranges of growth. All four genes complemented point and deletion mutants, with efficiencies that varied with temperature and ssb gene source. The SSBs are the largest bacterial SSBs identified to date (24.9-26.3 kDa) and may be divided into conserved amino- and carboxy-terminal regions and a highly variable central region. Greater amino acid sequence homology was observed between the SSBs as a group (72-87%) than with other bacterial SSBs (52-69%). Analysis of the amino acid composition of the SSBs revealed several features that could correlate with pressure or temperature adaptation. SSBs from the three low-temperature-adapted strains were an order of magnitude more hydrophilic than that from the mesophilic strain, and differences in the distribution of eight amino acids were identified which could contribute to either the temperature or pressure adaptation of the proteins. The SSBs from all four strains were overproduced and partially purified based upon their ability to bind single-stranded DNA. The differences found among the SSBs suggest that these proteins will provide a useful system for exploring the adaptation of protein-protein and protein-DNA interactions at low temperature and high pressure.


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