5. Genetics of Bacteria and Viruses

Synthesis of the amino acid histidine is a multistep anabolic pathway that uses the products of 13 genes (hisA to hisM) in E. coli. Two independently isolated  E. coli mutants, designated his1⁻ and his2⁻ are studied in a conjugation experiment. A his⁺ F' donor strain that carries a copy of the hisJ gene on the plasmid is mated with a his1⁻ recipient strain in Experiment 1 and with a his2⁻ recipient in Experiment 2. The exconjugants are grown on plates lacking histidine. Growth is observed among the exconjugants of Experiment 2 but not among those of Experiment 1.

Why is growth observed in Experiment 2 but not in Experiment 1?

Look closely at the consolidated Hfr map and the data used to build the map on page 261. Suppose a fifth Hfr strain had the F factor inserted exactly halfway between cysE and leuU and had an orientation that was the same as that of Hfr 1. List the order of gene transfer for the first six genes transferred by this Hfr and the number of minutes of conjugation at which each gene is expected to be seen.

A study was conducted in an attempt to determine which functional regions of a particular conjugative transfer gene (tra1) are involved in the transfer of plasmid R27 in Salmonella enterica. The R27 plasmid is of significant clinical interest because it is capable of encoding multiple-antibiotic resistance to typhoid fever. To identify functional regions responsible for conjugal transfer, an analysis by Lawley et al. [(2002). J. Bacteriol. 184:2173–2180] was conducted in which particular regions of the tra1 gene were mutated and tested for their impact on conjugation. Shown here is a map of the regions tested and believed to be involved in conjugative transfer of the plasmid. Similar coloring indicates related function. Numbers correspond to each functional region subjected to mutation analysis.

Accompanying the map is a table showing the effects of these mutations on R27 conjugation.

Effects of Mutations in Functional Regions of Transfer Region 1 (tra1) on R27 Conjugation
   R27 Mutation in     Conjugative       Relative Conjugation
         Region               Transfer                Frequency (%)
             1                          +                            100
             2                          +                            100
             3                          -                               0
             4                         +                             100
             5                         -                                0
             6                         -                                0
             7                         +                              12
             8                         -                                0
             9                         -                                0
           10                         -                                0
           11                         +                              13
           12                         -                                0
           13                         -                                0
           14                         -                                0

Which regions appear to have the most impact on conjugation? 

A study was conducted in an attempt to determine which functional regions of a particular conjugative transfer gene (tra1) are involved in the transfer of plasmid R27 in Salmonella enterica. The R27 plasmid is of significant clinical interest because it is capable of encoding multiple-antibiotic resistance to typhoid fever. To identify functional regions responsible for conjugal transfer, an analysis by Lawley et al. [(2002). J. Bacteriol. 184:2173–2180] was conducted in which particular regions of the tra1 gene were mutated and tested for their impact on conjugation. Shown here is a map of the regions tested and believed to be involved in conjugative transfer of the plasmid. Similar coloring indicates related function. Numbers correspond to each functional region subjected to mutation analysis.

Accompanying the map is a table showing the effects of these mutations on R27 conjugation.

Effects of Mutations in Functional Regions of Transfer Region 1 (tra1) on R27 Conjugation
   R27 Mutation in     Conjugative       Relative Conjugation
         Region               Transfer                Frequency (%)
             1                          +                            100
             2                          +                            100
             3                          -                               0
             4                         +                             100
             5                         -                                0
             6                         -                                0
             7                         +                              12
             8                         -                                0
             9                         -                                0
           10                         -                                0
           11                         +                              13
           12                         -                                0
           13                         -                                0
           14                         -                                0

What general conclusions might one draw from these data? 

A study was conducted in an attempt to determine which functional regions of a particular conjugative transfer gene (tra1) are involved in the transfer of plasmid R27 in Salmonella enterica. The R27 plasmid is of significant clinical interest because it is capable of encoding multiple-antibiotic resistance to typhoid fever. To identify functional regions responsible for conjugal transfer, an analysis by Lawley et al. [(2002). J. Bacteriol. 184:2173–2180] was conducted in which particular regions of the tra1 gene were mutated and tested for their impact on conjugation. Shown here is a map of the regions tested and believed to be involved in conjugative transfer of the plasmid. Similar coloring indicates related function. Numbers correspond to each functional region subjected to mutation analysis.

Accompanying the map is a table showing the effects of these mutations on R27 conjugation.

Effects of Mutations in Functional Regions of Transfer Region 1 (tra1) on R27 Conjugation
   R27 Mutation in     Conjugative       Relative Conjugation
         Region               Transfer                Frequency (%)
             1                          +                            100
             2                          +                            100
             3                          -                               0
             4                         +                             100
             5                         -                                0
             6                         -                                0
             7                         +                              12
             8                         -                                0
             9                         -                                0
           10                         -                                0
           11                         +                              13
           12                         -                                0
           13                         -                                0
           14                         -                                0

Which regions appear to have a limited impact on conjugation? <>