Specificity of the interactions between the Rep proteins and the origins of replication of Staphylococcus aureus plasmids pT181 and pC221 |
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Authors: | Serban Iordanescu |
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Institution: | (1) Department of Plasmid Biology, The Public Health Research Institute, 10016 New York, NY, USA |
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Abstract: | Summary pT181 and pC221 are closely relatedStaphylococcus aureus plasmids with the same genome organization, which is characterized by the overlapping of the origin of replication with the
sequence encoding a protein, Rep, essential for plasmid replication. Former results have shown the lack of in vivo cross-complementation
between these two plasmids, while in vitro studies have revealed the ability of both Rep proteins to act on either origin.
One possible explanation for this difference was based on a previous analysis of the incompatibility expressed by the origin
of replication of these plasmids, showing that the origin embedded in therep gene competes for Rep utilization with the origin of a test plasmid and that changes in the sequence of the origin reduce
its ability to compete. To avoid this problem, in the present work special hybrids were constructed in which the origin of
replication overlapping therep gene was mutationally inactivated, without changing the amino acid sequence of the encoded protein. The level of Rep expression
by these hybrids could be varied by taking advantage of what is presently known about the control of Rep synthesis in plasmid
pT181. The results of complenentation studies conducted using these hybrids have shown that: (i) at the usual level of expression
for a wild-type plasmid each Rep protein can initiate replication strictly from its corresponding origin; (ii) when overproduced,
the pT181 RepC protein could also act efficiently on the pC221 origin; a functional pT181 origin present in the same host
completely prevented this complementation; (iii) in excess, the RepD protein encoded by pC221 could replicate a plasmid carrying
the pT181 origin but could not ensure the hereditary stability of such a plasmid in the absence of another active replication
system; (iv) when overproduced both RepC and RepD could act on the origin of replication of three other related plasmids pS194,
pC223 and pUB112. |
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Keywords: | Plasmid pT181 Plasmid pC221 Rep proteins Replication origins Cross-complementation |
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