ANALYSIS OF SSB MUTATIONS IN-VIVO IMPLICATES SSB PROTEIN IN 2 DISTINCT PATHWAYS OF SOS INDUCTION AND IN RECOMBINATIONAL DNA-REPAIR

Site-directed mutations in the Escherichia coli ssb gene were tested f or the ability to complement a chromosomal ssb deletion for viability, and only the ssb W54->G mutation failed to do so at the pSC101 copy l evel. Non-aromatic amino acid substitutions for SSB Trp-54 (ssb W54->L and ssb W54->S) produced the greatest effects on in vivo protein func tion including altered marker linkage subsequent to generalized transd uction, extreme UV sensitivity, and a lack of ability to support SOS i nduction. Additionally, the ssb-113 (ssb P176->S) mutation demonstrate d the existence of both uvrA-dependent and uvrA-independent components of SOS induction. Although nucleotide excision repair appeared unaffe cted by alterations in the SSB protein, the mutational analysis sugges ts a direct role for SSB in recombinational repair.