RecJ exonuclease mutants of Escherichia coli

摘要

The RecJ protein of Escherichia coli is 5$spprime$-3$spprime$ single-strand specific exonuclease, known to play an important role in RecBC-independent recombination and UV-induced lesion repair. To gain further understanding of the biochemical mechanisms of RecJ, I have characterized three recJ mutants: recJ153, recJ77, and recJ147. The recJ153 allele affects gene expression and is a mutation of the translational initiation codon from GUG to GUA. I also characterized a second site suppressor of recJ153 known as srjA5. The srjA5 mutation is an allele of the infC gene which encodes the translation initiation factor IF3. The srjA5 mutation confers upon IF3 an inability to discriminate against abnormal start codons. The recJ77 allele is a loss of function mutation which localized next to a region of the RecJ protein that is conserved among other 5$spprime$ to 3$spprime$ exonucleases. This region of the protein may be part of the active site of the enzyme. The recJ147 allele is a temperature-sensitive mutant of recJ that was shown to have a reversible decrease in activity at the non-permissive temperature. Analysis of these mutants has significantly increased our understanding of the regions of the recJ gene that are important for its expression and activity.