Many viral oncogenes encode protein—yrosine kinase activities. However, important in vivo substrates of these enzymes have yet to be identified. Recently, type I topoisomerases were shown to be in vitro substrates for two tyrosine kinases. Following tyrosine phosphorylation, topoisomerase I activity was reduced 10-fold (Tse-Dinh et al. Nature312:785–786, 1984). To determine whether topoisomerase I activity was modulated by tyrosine phosphorylation in vivo, we have measured topoisomerase I activity in nuclear lysates prepared from both normal fibroblasts and cells transformed by two different viral oncogenes (v-abl, v-src). Under a variety of experimental conditions, we have found no evidence to support the notion that type I topoisomerase activity is modulated by tyrosine phosphorylation in vivo.
Rapid Communication| March 01 1986
A comparison of topoisomerase I activity in normal and transformed cells
W. H. Colledge;
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W. H. Colledge, M. Edge, J. G. Foulkes; A comparison of topoisomerase I activity in normal and transformed cells. Biosci Rep 1 March 1986; 6 (3): 301–307. doi: https://doi.org/10.1007/BF01115159
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