It has previously been predicted that the S45N and K44A mutants of dynamin are defective in the binding of GTP. This is on the basis of alignment with the S17N and K16N mutations in H-ras respectively5. During the early stages of our study we employed a simple filter-binding assay to screen mutant dynamins for their ability to bind [32P]GTPgS. We found that this assay was not very reproducible or quantifiable but we could clearly confirm qualitatively that, as predicted, S45N and K44A dynamin bind the nucleotide considerably less effectively than does WT dynamin (Fig. 2s). Also shown are some of the other mutants of dynamin that we believe bind normally to GTP on the basis of determination of their Kms (Table 1. main paper).
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