Table 1.

Frequency of Cro⁻ mutations generated during in vitro gap-filling replication

Protein composition	Mutation frequency × 10−5
Pol V (MBP-UmuC), UmuD′, RecA, SSB	2,325  ±  408
Component omitted:
UmuD′	27  ±  12
MBP-UmuC	19  ±  2.6
RecA	25  ±  3.6
SSB	51  ±  12
MBP-UmuC + MBP	18  ±  3.4
All proteins	8  ±  4
Pol III holoenzyme	98  ±  36
Pol III holoenzyme, UmuD′, RecA, SSB	81  ±  36
Pol I	138  ±  52
Pol I, UmuD′, RecA, SSB	78  ±  12
Pol II	148  ±  40
Pol II, UmuD′, RecA, SSB	65  ±  22

Gap-filling replication reactions were performed with the indicated proteins, after which the DNA products were introduced into an E. coli indicator strain and plated on lactose-eosin/methylene blue (EMB) plates. Mutant (dark-red) and wild-type (white) colonies were counted. Mutation frequency was calculated as described in Materials and Methods. Transformation of untreated intact pOC2 yielded a mutation frequency of 0.9 × 10⁻⁵.