ABSTRACT Streptococcus pneumoniae Rx1 is capable of repairing lesions caused by DNA-damaging agents in an error-free manner but lacks a UV-inducible error-prone repair system due to the absence of chromosomally encoded UmuDC-like proteins. We have identified an operon-like structure 8 kb from the left end of the pneumococcal conjugative transposon Tn 5252 that confers SOS function in the host cells. DNA sequence analysis of this region revealed the presence of four open reading frames (ORFs). The deduced amino acid sequence of one of them, ORF13, which is capable of encoding a protein of 49.7 kDa, showed significant homology to UmuC, MucB, and other proteins involved in the SOS response. The carboxy-terminal region of another, ORF14, which is predicted to encode a 26-kDa polypeptide, shared similarity with UmuD- and MucA-like proteins that carry the amino acid residues recognized by the activated RecA* protein for proteolytic cleavage. The presence of plasmids carrying subcloned DNA from this region was found to restore UV-inducible mutagenic repair of chromosomal DNA in Escherichia coli cells defective in error-prone repair as well as in pneumococcus and Enterococcus faecalis UV202. Mutations within ORF13 abolished UV-induced mutagenesis but did not affect the conjugal transposition of the element.