Identification of protein X of Escherichia coli as the recA+/tif+ gene product. |
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Authors: | Peter T Emmerson and Stephen C West |
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Institution: | (1) Department of Biochemistry, University of Newcastle upon Tyne, NE1 7RU Newcastle upon Tyne, England |
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Abstract: | Summary Protein X, molecular weight 40,000, has been separated from the other proteins of E. coliby a two-dimensional gel electrophoretic technique which separates proteins according to isoelectric point (pI) in the firstdimension and according to molecular weight in the second. When protein X is induced in wild-type cells by mitomycin C treatmentit has a pI6.0. However, when protein X is induced in a tif-1 mutant, either by temperatureshift-up to 42° or by mitomycin C treatment at 30°, it has a pI6.2. The low level of protein X which is present inuninduced tif mutants at 30° also has a pI6.2. These results suggest thattif-1 is a mis-sense mutation in the gene coding for protein X. Since transduction andcomplementation studies indicate that tif-1 is a mutation of therecA
+
gene (Castellazzi, Morand, George and Buttin, 1977) it follows that protein X is the recA
+ gene product.A model has been formulated to account for the relationship between protein X synthesis and the recA
+
and lexA
+
genes. In this model, a repressor coded by lexA
+
binds to the operator of the recA
+
gene from whence it can normally only be removed by the combined action of an inducer and protein X, the recA
+ product. Thus, protein X controls its own synthesis. The tif-1 mutation leads to a temperature sensitive form of protein X which, at 42°, can spontaneously remove the repressor without the intervention of the inducer. |
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Keywords: | |
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