CLONING AND SEQUENCING OF THE PROTEUS-MIRABILIS GENE FOR A SINGLE-STRANDED DNA-BINDING PROTEIN (SSB) AND COMPLEMENTATION OF ESCHERICHIA-COLI SSB POINT AND DELETION MUTATIONS

The gene of Proteus mirabilis coding for a single-stranded DNA-binding protein (SSB) was cloned in Escherichia coil from a genomic library. It restored the UV resistance and the rate of cell division of an E. c oil ssb-113 mutant to the same extent as the cloned E. coil ssb(+) gen e did. An E. coli mutant with deleted ssb was viable with the P. mirab ilis ssb(+) gene provided on a single-copy-number plasmid and had the same cell division rate as with the E. coli ssb(+) gene on the same ve ctor plasmid. The recovery from UV damage of an excision repair defici ent (uvrA) mutant deleted for the ssb gene was identical with the ssb( +) gene from P. mirabilis or E. coil, suggesting full substitution in recombinational DNA repair of the homologous by the heterologous SSB p rotein. The nucleotide sequence of the gene revealed that the SSB has 81% amino acid sequence homology with the E. coil SSB and only 58-63% with various plasmid SSBs. The data provide evidence that the bacteria l chromosomally coded SSBs and the plasmid encoded SSBs constitute sep arate groups.