Biology Reference
In-Depth Information
85
= 0.255,
and
= 0.171 .
Multiplying the above values of and by the length of the DNA in the
transducing particle or 2 min, we have the separation between genetic
markers A and B being approximately 0.51 min and that between markers B
and C 0.34 min.
Escherichia coli
GENETIC MAP
Taylor (1970) started to examine the genetic markers of
E. coli
carefully and
constructed a linkage map. At that time, the entire length of the
E. coli
chromosome was assumed to be 90 minutes in length. That map was re-
calibrated in 1976 by Bachmann
et al.
As more and more genetic markers
were identified, Bachmann (1983, 1990) have been incorporating all
available genetic markers of
E. coli
into the linkage map using tranduction
experiments and the above derived equations. She had positioned a total of
1,403 of them on the
E. coli
chromosome by 1990. During the past ten
years, even more genetic markers have been identified (see the special
website at Yale University, <http://cgsc.biology.yale.edu >). As an example,
the section of the
E. coli
chromosomal map from 0.0 minute to 1.0 minute is
shown in Fig. 3-10. This information has provided a useful guide to the
sequencing of
E. coli
genome (see, for example, Itoh
et al.,
1996).
Recently, both the traditional map (Berlyn, 1998) and the physical map
(Rudd, 1998) have been summarized. Other websites can be found from the
above website and are also listed by Rudd (2000).
The physical map (Rudd, 1998) consists of restriction enzyme sites and
positions of cloned segments of
E. coli
chromosome in lambda phage
EMBL4 (Kohara
et al
., 1987). It has been correlated with the 4,639,221 bp
DNA sequence of
E. coli
K-12 strain MG1655 version M52 (Blattner
et al
.,
1997). The
thr A
gene has been sequenced (Katinta
et al
., 1980) and was
physically positioned near the beginning of the DNA sequence by
convention (Blattner
et al
., 1997)
