The circular form has 'nicks' 12 nucleotides apart which are joined by polynucleotide ligase. The circular intermediate is opened at a different point and inserted at a particular point on the E.coli chromosome by the viral enzyme integrase to form a lysogenic chromosome. The gene order now becomes 3, 4, 1, 2, a cyclic permutation of the orginal gene order I, 2, 3, 4.
After
several
generations
the
chromosome
may
enter
the
lytic
phase
as
a
result
of
induction
by
radiation
or
chemical
compounds.
The
enzymes
integrase
and
excisionase
catalyse
the
excision
of
the
lambda
DNA
from
the
E.
coli
chromosome.
