Chimeric mutational vectors

A method of introducing a change in a target DNA sequence to form a different, desired sequence in a recombination/repair competent prokaryotic cell comprising:

• (A) transforming the prokaryotic cell with a duplex mutational vector comprising:
• (i) a first oligonucleobase strand of at least 12 linked nucleobases and not more than 75 linked nucleobases, that has a first and a second terminal nucleobase;
• (ii) a second oligonucleobase strand having a 3′ most and a 5′ most nucleobase and having a number of nucleobases equal to the first oligonucleobase strand, which second oligonucleobase strand is optionally divided into a first chain and a second chain;
• and
• (iii) a single 3′ end nucleobase and a single 5′ end nucleobase;
• in which
• (a) the 3′ most and 5′ most nucleobases of the second oligonucleobase strand are Watson-Crick base paired to the first terminal and the second terminal nucleobase of the first oligonucleobase strand, respectively,
• (b) said 3′ most nucleobase and said second terminal nucleobase are protected from 3′ exonuclease attack;
• and
• (c) the second oligonucleobase strand contains at least two non-overlapping regions of at least 5 contiguous nucleobases that are Watson-Crick base paired to nucleobases of the first oligonucleobase strand,
• provided that for not more than two contiguous nucleobases of a strand is a deoxy-type nucleobase Watson-Crick paired with a ribo-type nucleobase or a ribo-type nucleobase Watson-Crick paired with a deoxy-type nucleobase;
• and
• wherein the sequence of at least one oligonucleobase strand comprises the different, desired sequence;
• and
• (B) detecting the presence of the different desired sequence from or in the prokaryotic cell or progeny thereof.