RESOLUTION OF HOLLIDAY JUNCTIONS IN ESCHERICHIA-COLI - IDENTIFICATION OF THE RUVC GENE-PRODUCT AS A 19-KILODALTON PROTEIN

The ruvC gene of Escherichia coli specifies a nuclease that resolves Holliday junction intermediates in genetic recombination (B. Connolly, C. A. Parsons, F. E. Benson, H. J. Dunderdale, G. J. Sharples, R. G. Lloyd, and S. C. West, Proc. Natl. Acad. Sci. USA 88:6063-6067, 1991). The gene was located between aspS and the ruvAB operon by DNA sequencing and deletion analysis of ruvC plasmids and was shown to encode a protein of 18,747 Da. Analysis of the DNA flanking ruvC indicated that the gene is transcribed independently of the LexA-regulated ruvAB operon and is not under direct SOS control. ruvC lies downstream of an open reading frame, orf-33, for a protein which migrates during sodium dodecyl sulfate-polyacrylamide gel electrophoresis as a 33-kDa polypeptide. These two gene probably form an operon. However, expression of ruvC was found to be very poor relative to that of orf-33. A double ribosomal frameshift between these genes is proposed as a possible reason for the low level of RuvC. Two further open reading frames of unknown function were identified, one on either side of the orf-33-ruvC operon.