Escherichia coli strains harbouring pbpAts mutations are particularly sensitive to functional alterations of penicillin-binding protein 2 (PBP 2) at the initiation of growth. Shift-up to 42°C results in the inability of cells to reach a steady rate of growth and division. Furthermore, a very high proportion of cells generate minicell-like structures which are pinched-off through a process requiring the activity of penicillin-binding protein 3 (PBP 3).