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Mol. Cell. Biol., 03 1996, 968-976, Vol 16, No. 3
M Benard, C Lagnel, D Pallotta and G Pierron
We analyzed the replication of two unlinked actin genes, ardB and ardC ,
which are abundantly transcribed in the naturally synchronous plasmodium of
the slime mold Physarum polycephalum. Detection and size measurements of
single-stranded nascent replication intermediates (RIs) demonstrate that
these two genes are concomitantly replicated at the onset of the 3-h S
phase and tightly linked to replication origins. Appearance of RIs on
neutral-neutral two-dimensional gels at specific time points in early S
phase and analysis of their structure confirmed these results and further
established that, in both cases, an efficient, site-specific, bidirectional
origin of replication is localized within the promoter region of the gene.
We also determined similar elongation rates for the divergent replication
forks of the ardC gene replicon. Finally, taking advantage of a restriction
fragment length polymorphism, we studied allelic replicons and demonstrate
similar localizations and a simultaneous firing of allelic replication
origins. Computer search revealed a low level of homology between the
promoters of ardB and ardC and, most notably, the absence of DNA sequences
similar to the yeast autonomously replicating sequence consensus sequence
in these Physarum origin regions. Our results with the ardB and ardC actin
genes support the model of early replicating origins located within the
promoter regions of abundantly transcribed genes in P. polycephalum.
Copyright © 1996, American Society for Microbiology
Mapping of a replication origin within the promoter region of two unlinked, abundantly transcribed actin genes of Physarum polycephalum
Laboratoire Organisation Fonctionnelle du Noyau, Villejuif, France.
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