Illusory defects and mismatches: why must DNA repair always be (slightly) error prone?

There is growing evidence that recombination is mu;tagenic and that some forms of DNA repair synthesis are error prone. DNA synthesis in mismatch repair might also be error prone. DNA-repair systems detect structural defects in DNA with high efficiency but they occasionally also strike at normal sections of DNA. Considering the diversity of local DNA structure, some DNA sections with complementary sequences are bound to act as preferential false targets for a repair system (i.e. as "illusory defects"). However, if the repair system never changes the sequence upon repair, it will be solicited again and again by the illusory defect, a potentially harmful situation. It is therefore advantageous for a repair system to be, to some extent, error prone. Strong illusory defects may arise at the decanucleotide level and could be the cause of local increases in mutation levels. They might be used to initiate somatic hypermutation pathways. Copyright 2000 John Wiley & Sons, Inc.