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 coli from a genomic library. It restored the UV resistance and the rate of cell division of an E. coli ssb-113 mutant to the same extent as the cloned E. coli ssb+ gene did. An E. coli mutant with deleted ssb was viable with the P. mirabilis 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 vector plasmid. The recovery from UV damage of an excision repair deficient (uvrA) mutant deleted for the ssb gene was identical with the ssb+ gene from P. mirabilis or E. coli, suggesting full substitution in recombinational DNA repair of the homologous by the heterologous SSB protein. The nucleotide sequence of the gene revealed that the SSB has 81% amino acid sequence homology with the E. coli SSB and only 58-63% with various plasmid SSBs. The data provide evidence that the bacterial chromosomally coded SSBs and the plasmid encoded SSBs constitute separate groups.