a question about post-translational modification - (Dec/02/2011 )

Are there post-translational modifications in prokaryotes?

If not, what are the "signal peptides" for in prokaryotes?

Yes, phophorylation, lipid and glyco modifications all occur, as well as cyclization of peptides and other side chain modifications.

"If not, what are the "signal peptides" for in prokaryotes? "

Well one function is to direct the protein for secretion via the appropriate secretion system....check out the twin-arginine translocation system in bacteria for an example....