CONCLUSION

The analysis of three mutants of the hsdS gene revealed that the central conserved region plays a very important role in protein-protein interactions during the assembly of the endonuclease.

1. The Res Mod phenotype and the insolubility of the deleted subunit HsdSDXN , when co-produced with HsdM, indicates that the presence of only one copy of the repeated amino acid sequence (in the C-terminal conserved domain) is not sufficient for the assembly of HsdS and HsdM.

2. The hsdS72 and hsdS123 are the first description of a non- classical mutations in the hsdS gene of the EcoRl24I R-M system. These mutations probably alters the assembly of the endonuclease in such a way as to prevent DNA cleavage but allows methylation.

Both mutants resulted from a single amino acid change, Trp212 to Arg (hsdS72) and Lys184 to Asn (hsdS123).

The location of the single amino acid change in the central conserved region or at its border suggests that this region is extremely important for the assembly of the methylase with HsdR.

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© University of Portsmouth
Author Dr Keith Firman,
Page last updated September 28, 2008