VIABILITY AND PRELIMINARY IN-VIVO CHARACTERIZATION OF SITE-DIRECTED MUTANTS OF ESCHERICHIA-COLI SINGLE-STRANDED DNA-BINDING PROTEIN

Site-directed mutations involving selected amino acids of Escherichia coli single-stranded DNA-binding protein (SSB) were tested for their i n vivo functionality when introduced into a chromosomal ssb deletion s train on a plasmid. All mutants complemented the ssb deletion for viab ility when present on a pSC101 derivative. The generation time with ss bW54S doubled in comparison to the ssb+ control, and both the ssbW54S- and ssbH55K-containing strains exhibited temperature sensitivity. ssb H55K, ssbW54S, ssbW88T, and ssbH55Y (ssb-1) strains displayed reduced survival to ultraviolet irradiation, while ssbW40T and ssbF60L strains were comparable to the ssb+ control strain. This study represents the first investigation of the in vivo properties of ssb mutations constr ucted for in vitro analysis of DNA binding by SSB.