Aberrant DNA replicative intermediates.
When DNA is isolated from rapidly dividing Drosophila Melanogaster eggs
at the preblastoderm stage (where the doubling time is only about 9 min). a
high proportion of replicative intermediates can be observed. Amongst
these are significant numbers of aberrant types in which the replicated area
has apparently branched migrated to give structures of the type shown to the
right and in diagrammatic form in diagram (b) below.
In this particular study (Inman RB. Biochimica et Biophysica Acta 1984
783 205-215) the eggs were grown under reasonably stress free conditions.
but in other studies of DNA replication in E.coli, B.Subtilis and
bacteriophage lambda various types of aberrant replicative growing forks
were also observed and thought to have arisen as a result of a
replicative repair process (see below).
The drawings (c) and (d) show the form of the aberrant intermediates observed
in E.coli, B.subtilis and Lambda phage. In all these cases, the cause of
the aberrant types was traced to the thymine deprivation conditions used
in the growth of the bacteria, under normal growth conditions such
aberrations were not observed. Similar experiments on lambda phage
replicative intermediates derived from infections of E.coli, unable to
provide SOS functions (RecA144 or LexA3), showed abnormal replicative
intermediates, but in much reduced numbers. Apparently the aberrant
replication forks result from some type of replicative repair pathway.
Valenzuela MS and Inman RB. Molec gen Genet (1978) 245-249.
Valenzuela MS & Inman RB, Mol Gen Genet 1981 184 450-456.
Valenzuela MS & Aquinaga M. Mol Gen Genet 1981, 181 241-247
Valenzuela MS & Inman RB, BioChem. BioPhy. Research Comm. 1986 137 869-875
Aberrant bacteriophage lambda replication under SOS conditions.
The drawing in (e) shows the aberrant types found at considerable
frequency under SOS conditions. It was shown that both the primary and
secondary initiations started at the ori position in the lambda genome.
In some cases only one daughter origin reinitiated, in others both had
reinitiated as shown in the drawing.
In other experiments we have shown that normally, lambda reinitiation is
a tightly controlled process that does not allow reinitiation while a round
of replication is in progress. Under SOS conditions this control is in some
way lost.
Schnos M & Inman RB. J. Mol.Biol. (1982) 457-465
Schnos M & Inman RB. Virology (1985) 145 304-312
Schnos M & Inman RB
Virology (1987) 158 294-299
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