Isolation and genetic analysis of amber uvrA and uvrB mutants

Expression of the uvrB gene of Escherichia coli: in vitro construction of a pMB9 uvrB plasmid

Bacteriophage lambdab2att2 [lambdab2cI857intam6(deltabioAB)bioFCD+uvrB+phr+] codes for a function(s) that confers UV resistance (Uvr+) and reactivation of irradiated phage (Hcr+) to an Uvr-Hcr-Escherichia coli strain. It was demonstrated that these functions are expressed under the control of bacterial regulatory elements located on lambdab2att2 DNA. The location of the E. coli uvrB gene on the DNA of this transducing phage was established by heteroduplex and restriction-enzyme analyses. Recombinant DNA molecules were constructed in vitro from plasmid pMB9 (Tcr), as the vector, and an EcoRI fragment (Eco-RI-F) of lambdab2att2 DNA. The resulting plasmid, designated pNP5, has a molecular weight of 5.1 X 10(6) and replicates in a relaxed fashion. Transformation of E. coli uvrB with plasmid pNP5 resulted in clones that are Uvr+ Tcr. Irradiation of bacteria transformed with plasmid pNP5 with low UV doses revealed a complete restoratation of the Uvr+ phenotype by the presence of the cloned EcoRI-F DNA, while only a partial restoration was observed after irradiation with high UV doses. Likewise, the Hcr+ character was also partially restored due to the presence of pNP5. No correlation was found between the acquired Uvr+, Hcr+ properties, and the presence of correndonuclease II activity in an extract of bacteria that harbor plasmid pNP5.

Evidence that the gene uvrB is indispensable for a polymerase I deficient strain of Escherichia coli K-12

Conclusive evidence in presented to show that the gene uvrA is dispensable, but the uvrB is indispensable for an Escherichia coli strain carrying gene polA1. We constructed strains E139 (sup-126 polAl uvrB59) and E159 (sup-126 polAl uvrA43) where mutations polAl, uvrB59 and uvrA43 are amber mutations and mutation sup-126 is an amber suppressor mutation effective at 30 degrees C but not at 42 degrees C. At 42 degrees C, strain E139 is inviable but strain E159 viable whereas both are viable at 30 degrees C. Revertants of E139 viable at 42 degrees C occurred spontaneously at a frequency of about 3 X 10(-4). One of the revertants was shown to be caused by suppressor mutation, designated spu, rather than back mutation of the gene uvrB59 or polAl or amber suppressor mutation. Viabilities of the revertants varied from 10(-3) to 1.0 at 42 degrees C compared with those of 30 degrees C. At 42 degrees C, all the revertants with normal viabilities at 42 degrees C were non-filamentous in contrast to the filamentous character of E139. However, strain E159 was viable at 42 degrees C despite its filamentous character. We conclude that the gene uvrB is involved not only in excision repair but also in normal growth in a polA background.