What we know about the competence-regulon gene comM

The grad student of an upstairs colleague has been doing a lot of excellent work on the Rhodobacter capsulatus homologs of some H. influenzae competence genes, because he has discovered that they are also needed for gene transfer by GTA, the phage-related 'gene transfer agent'.

One of the genes he's looking at is comM.  ComM is predicted to be a cytoplasmic protein, a member of the YifB subfamily of AAA-ATPase proteins.  Here's a review about the AAA+ superfamily.  These proteins have a very diverse range of activities, so it's hard to make any prediction about a likely function for ComM from looking at its relatives.

ComM was originally studied in H. influenzae, by Michelle Gwinn and Jean-Francois Tomb in Ham Smith's lab.  They reported that their comM mutant had normal DNA uptake but reduced transformation (down about 300-fold).  It had normal expression of a lacZ fusion to another competence gene, indicating that it didn't affect regulation of competence.  (It also had reduced phage recombination, but we still don't know what this assay means.)

To find out why transformation was reduced, they followed the fate of end-labelled DNA fragments. The kinetics were like those of both wildtype cells and a rec1 mutant (rec1 is the H. influenzae homolog of E. coli's recA; it's absolutely needed for homologous recombination). So the authors concluded that the comM knockout does not affect the transport of DNA into the cytoplasm.  But their data doesn't distinguish between an effect on DNA degradation (indirectly preventing recombination) and a direct effect on recombination.

We've independently created a comM knockout; its DNA uptake is also normal, and its transformation is also down, but only about 20-fold.  We haven't done anything more to evaluate its phenotype.



*Interestingly, Gwinn et al. commented that "In addition, HI1117 has homology to a magnesium chelatase gene of Rhodobacter capsulatus, bchI, involved in bacteriochlorophyll biosynthesis (1) and to related genes from other photosynthetic organisms."